1  For many years, the workings and the jurisprudence of international courts and tribunals (‘ICTs’) have been at the heart of international legal scholarship. By comparison, international relations (‘IR’) scholars in political science have historically paid little attention to ICTs, such as the Permanent Court of International Justice (PCIJ) and the International Court of Justice (ICJ), which were seen through the prevailing realist lens as being of little or no importance in global politics. In recent decades, however, IR scholars have taken up the study of international courts, driven both by the diversification of available IR-theoretical frameworks and by the empirical proliferation of international courts in the post-Cold War era. In the process, IR scholars have made substantial contributions, applying a distinctive set of theoretical lenses to questions about the design, behaviour, independence, and viability of these courts.

2  The aim of this entry is to examine the four core traditions of IR theory as applied to ICTs, and to identify the value-added insights as well as the lacunae of this research. The entry proceeds in four sections. Following this introduction, section B below explores four great traditions in IR theorizing about international adjudication, focusing in turn on realism, institutionalism, liberalism, and constructivism. Building on this theoretical basis, section C identifies four substantive, value-added contributions of IR to the study of international adjudication, organized under the rubrics of institutional design, the behaviour of litigants, judicial behaviour and independence, and the dynamic evolution of international adjudication systems over time, including both positive feedbacks and progressive development as well as negative feedbacks and backlash. A brief section D concludes.

3  Much of the distinctive contribution of IR to the study of international adjudication arises from the application of IR theories, which generate theoretical concepts, questions, and hypotheses that are largely ignored in much international legal scholarship. With a few exceptions, the IR literature on international courts has been informed primarily by off-the-shelf theories of IR. In the immediate post-war era, realist theory largely dominated the IR literature, and many legal scholars still implicitly or explicitly associate IR as a field with the post-war realist critique of international law as insignificant or epiphenomenal (Koskenniemi, 2009a, 2009b). Yet contemporary IR scholarship is theoretically pluralist, with major strains of realist, institutionalist, constructivist, and liberal theories co-existing in the discipline, and each of these strains has approached the subject of international law and international adjudication in distinctive ways. (This entry, echoing Dunoff and Pollack, 2013, examines only the four ‘mainstream’ IR theories; for good reviews of critical theories, which have exerted direct influence within the international legal academy as well as in IR, see eg Cox, 1981; Wyn-Jones, 2000; Reus-Smit and Snidal, 2010). A complete review of these theories is beyond the scope of this entry, but a brief discussion of the four theories and their application to international courts will illustrate both the diversity of, and insights from, IR theory for the study of international adjudication.

4  Among IR theories, realism is widely, and accurately, seen to be particularly hostile to the idea that international law can meaningfully constrain states’ pursuit of their individual self-interest. In the realist approach, the international system is characterized by anarchy, self-help, and the necessary pursuit of power, and the key players are states, with other actors (including international organizations and international courts) playing at best a secondary role. In such a world, post-war realists argued, state power was the primary determinant of political outcomes, and statesmen and women driven by a relentless concern for the national interest and national security would be unwise to place their hopes in what Hans Morgenthau (1948) called the ‘legalism-moralism’ that had dominated the literature during the interwar period. Perhaps for this reason, post-war realists largely ignored international law, which was seen as epiphenomenal, reflecting the interests of the great powers and exerting no causal force independent of those powers (Waltz, 1979). Furthermore, international courts during the Cold War era were relatively few and, outside of the European Union (‘EU’) (which was seen as an aberration explained in large part by United States protection and not as a harbinger of broader developments in IR), enjoyed only minuscule caseloads, seemingly supporting the realist claim that they were at best minor players on the global stage.

5  For this reason, realist theory is often seen as essentially irrelevant to the study of international law and courts. Nevertheless, as Richard Steinberg (2013, 50) argues, realism does offer a coherent account of international law, emphasizing state interests and state power as the context for all international law-making, interpretation, and application. In this view, states negotiate treaties and other international legal agreements out of concern for their own self-interests, and the terms of those agreements are skewed to reflect the interests of the most powerful states. Realists do not, therefore, dispute that international courts are sometimes established by states, that they engage in a process of legal interpretation, that they sometimes rule against powerful states in individual cases, or even that powerful states may comply with adverse rulings in light of the overall benefits of membership in international regimes whose terms tend to favour them (Steinberg, 2013, 164; Garrett, 1992; Garrett and Weingast, 1993). In a realist view, however, any international court is ultimately embedded in an international system characterized by unequal distribution of power, and powerful states retain the ability to ignore or sanction any international court that rules against its vital interests. Furthermore, rational and strategic international courts are likely to anticipate and accommodate the vital interests of great powers and interpret the law in such a way as to avoid noncompliance or backlash. Hence, in the long run, ‘interpretation replicates power’ (Steinberg, 2013, 163).

6  The realist view of both international law and courts has found a foothold in international legal studies, largely through the works of Jack Goldsmith and Eric Posner (2005), who offered an account of The Limits of International Law that was billed as a rational choice theory, but drew many of its core assumptions from traditional realism (Hathaway and Lavinbuk, 2006). In his 2009 book The Perils of Global Legalism, Posner (2009, xii) goes further, echoing Morgenthau in assailing his legal colleagues’ commitment to ‘legalism’, which he defines as ‘an excessive faith in the efficacy of international law’ despite the latter’s ‘weak and unreliable’ character and institutions. Scholars in this tradition have argued that international courts both are, and should be, dependent on states rather than independent (Posner and Yoo, 2005), and that great powers will ultimately ‘work around’ activist courts and unwelcome rulings, constructing new tribunals that can be more easily controlled (Posner, 2009, xiv).

7  Growing out of realism, but departing from it in several key assumptions, is the ‘modified structural realist’ theory known in contemporary scholarship as neoliberal institutionalism or rational-choice institutionalism, sometimes referred to simply as institutionalism (for good introductions, see Keohane, 1984, 1989; Martin and Simmons, 2001; Stein, 2008; Koremenos, 2013; on the historical institutionalist offshoot from this literature, see Fioretos and others, 2016; Fioretos, 2018).

8  Like realist theory, rational-choice institutionalism posits an anarchic world of unitary, self-interested states. Unlike realists, however, institutionalists argue that international institutions can help states cooperate under anarchy, at least under certain specified conditions, by performing a number of useful functions. At the negotiating stage, for example, international institutions can reduce the transaction costs of negotiating international agreements, by providing fora for regular meetings of officials. At the implementation stage, international regimes can address the core cooperation problems identified by Prisoner’s Dilemma and collective action models, by providing iteration and information about state compliance, reducing the prospects of reneging, and increasing the credibility of cooperative commitments (Krasner, 1983; Keohane, 1984, 1989; Hasenclaver and others, 1997). International institutions such as the United Nations or the World Trade Organization (‘WTO’), for example, can turn a one-shot Prisoner’s Dilemma into an iterated, or repeated, game; under such circumstances, states can cooperate through ‘tit for tat’ strategies that reward cooperation and punishing defection from previous rounds (Axelrod, 1984). International institutions can also ameliorate collective action problems by monitoring Member State compliance with their provisions, reporting instances of non-compliance, and, in some cases, providing third-party dispute settlement (Keohane and others, 2000; Raustiala and Slaughter, 2001).

9  Although the early institutionalist work on international cooperation arguably overlapped heavily with the study of international law, institutionalist scholars of the 1980s and 1990s deliberately de-emphasized the legal nature of the norms and rules they studied. By the 1990s, however, a number of legal scholars had begun to identify the promise of institutionalist theory for those seeking to understand the workings of international law (Abbott, 1989; Slaughter Burley, 1993), and a collective project on the legalization of world affairs established a widely debated framework and opened the floodgates for political science scholarship on international law. This ‘legalization’ project sought to provide a framework for studying the causes and effects of international law, which the project leaders defined in terms of three fundamental properties: obligation (whether a norm or rule is considered binding on states), precision (the clarity of states’ responsibilities in a given agreement), and delegation (particularly of dispute-settlement powers to a third-party international court or arbitrator) (Abbott and others, 2000). All else being equal, international agreements with high values for obligation, precision, and delegation were considered to be ‘hard law’, which could be costly to conclude but had significant advantages in terms of enhancing compliance, while those with lower values fell toward the ‘soft’ end of the spectrum, being easier to negotiate and more flexible in response to change (Abbott and Snidal, 2000; Pollack and Shaffer, 2009). The legalization framework proved controversial, with constructivist scholars arguing that such an instrumental approach to law missed its essential normative features (Finnemore and Toope, 2001; Reus-Smit, 2004), but the revived focus on law has led to a renaissance of IR scholarship on international law (Hafner-Burton and others, 2012), and to the birth of a new, interdisciplinary IL/IR (international law/international relations) field (Dunoff and Pollack, 2013).

10  With respect to the making of international law, the dominant approach has been the so-called rational-design approach (Koremenos and others, 2001; Koremenos, 2016), which has focused on identifying the conditions under which states adopt specific types of legal understandings, including treaties and customary international law (Guzman, 2008), exit clauses (Helfer, 2005, 2013), safeguard clauses (Rosendorff and Milner, 2001; Helfer, 2013; Pelc, 2016), reservations (Swaine, 2006; Helfer, 2006; Neumayer, 2007), and—of particular importance for our purposes here—third-party dispute settlement (Keohane and others, 2000; Rosendorff, 2005; Koremenos, 2007; Koremenos and Betz, 2013; Koremenos, 2016).

11  With respect to the application and adjudication of international law, the rational-choice tradition has fostered an explosion of work, considered in greater detail below, on the autonomy and independence of international secretariats and courts, which is seen to vary considerably as a function of their institutional statutes or frameworks as well as the preferences of their state ‘principals’ (see eg Alter, 1998, 2008; Stone Sweet and Brunell, 1998, 2012; Voeten, 2008; Carrubba and others, 2008, 2012; Carrubba and Gabel, 2015; Elsig and Pollack, 2014; and Squatrito, 2018).

12  Yet another strand of rational-choice institutionalist work focused on what political scientists have called regime complexity, defined as ‘an array of partially overlapping and nonhierarchical institutions governing a particular issue-area’ (Raustiala and Victor, 2004, 279; Alter and Raustiala, 2018). According to these studies, the specific regime or venue chosen to deal with a given problem is likely to affect substantive outcomes in that area, and for this reason states are likely to engage in forum shopping, selecting particular regimes that are likely to support their preferred outcomes. Subsequent work in this tradition has demonstrated that states do indeed attempt to shop among existing regimes, shift responsibility for questions from one regime to another, and even create new regimes that are more congenial to their interests than existing institutions (Helfer, 2004; Jupille and others, 2013). While IR scholars have mostly focused on state forum shopping with respect to international law-making, international legal scholars studying the related concept of ‘legal fragmentation’ have focused on the dual problems of state choice of jurisdiction for international litigation, as well as the dilemmas posed for international courts ruling in areas where their substantive jurisdiction overlaps with those of other courts (Koskenniemi and Leino, 2002; Boisson de Chazournes, 2018).

13  Rational-choice institutionalism, therefore, has created a promising and highly influential set of theoretical frameworks and research agendas for the study of international law. In doing so, however, institutionalists, like realists, relied on the convenient yet questionable assumption that states are unitary rational actors with fixed preferences. The past two decades, by contrast, have witnessed the revival of a liberal tradition that, unlike institutionalism, rejected the notion of states as unitary rational actors and sought to ground the study of international cooperation and conflict in a theory of state-society regulation that seeks to explain the origins of, and variation in, national preferences as a prelude to modelling the interactions among those states. In its most influential formulation, by Andrew Moravcsik (1997), liberalism can be said to rest on three broad assumptions: (1) the primacy of societal actors, who place policy demands on governments; (2) the importance of representative institutions, which act as a ‘transmission belt’ aggregating societal interests with greater or lesser fidelity or bias depending on regime type (eg, authoritarian vs democratic) and other domestic institutions (eg electoral and party systems); and (3) the configuration of interdependent state preferences, which determine the nature of the ‘game’ being played by states at the international level. Put simply, liberalism is a two-stage, bottom-up approach that focuses on societal interests and their aggregation into a putative national interest in the first stage, and subsequently examines the interactions among states in the second stage.

14  Stated in such broad terms, liberalism is a loose framework for analysis, or what Alexander Wendt (1999) has called a ‘second-order theory’, but several efforts have been made to specify substantive ‘first-order theories’ of international cooperation based on liberal assumptions. Three of the most influential liberal theory contributions in IR have been Robert Putnam’s (1988) ‘two-level games’ model of international negotiations, Moravcsik’s (1998) ‘liberal intergovernmentalist’ theory of European integration, and David Lake’s (2008) ‘Open Economy Politics’ approach to international political economy. The implications of the liberal approach for international law are also important, and were first explored systematically by Anne-Marie Slaughter (1993), who derived specific, testable hypotheses from liberal IR theory for the study of international law, focusing in particular on the systematic differences in commitment and compliance between liberal, democratic states on the one hand, and illiberal, authoritarian regimes on the other.

15  Liberal scholarship in the two decades since Slaughter’s classic article has established that the making of, interpretation of, and compliance with international law all are influenced substantially by domestic politics. In terms of law-making, the substantive preferences of interest groups in domestic society are aggregated with greater or lesser degrees of bias into national preferences by domestic institutions, and these national preferences in turn determine the constellation of state preferences, and hence the form and substance of international legal agreements (Moravcsik, 2013, 87–95).

16  Moving to the interpretation of law, liberal scholars have innovated within IR theory by shining a light on the interaction of international courts with domestic actors inside of states, including individual litigants at the litigation stage, as well as ‘compliance constituencies’ after an international court ruling. In this, they have taken inspiration largely from the legal system of the EU, in which individual litigants can bring cases under EU law in their domestic courts, without national-government gatekeeping, and in which national courts can then request a ‘preliminary ruling’ from the European Court of Justice (‘ECJ’) on the reading of EU law, which is then applied and enforced within national legal systems (Mattli and Slaughter, 1995; Alter, 1998; Preliminary Ruling: European Court of Justice (ECJ)). Systematizing these features, Slaughter and Helfer (1997), and later Keohane and others (2000), offered theoretical frameworks for analysing the relations between international or supranational courts on the one hand, and domestic legal actors on the other.

17  Generalizing from supranational courts to the broader universe of international courts, Keohane and others (2000) offer a framework in which international courts can be characterized along three dimensions: access (limited to state governments or granted to individual litigants), independence (of the international court from its Member State principals), and embeddedness (the extent to which international court rulings are accepted and enforced by national courts within the national legal order). Courts that scored low on each of these three dimensions are referred to as ‘interstate courts’, such as the ICJ, where national governments served as gatekeepers with considerable control over the docket of the court and compliance with its rulings. By contrast, courts that score high on these three dimensions are considered ‘transnational courts’, to which individuals can bring cases (including large numbers of cases, potentially inconvenient for national governments), and in which countries seeking to defy international court rulings would have to defy not only those courts but their own domestic courts as well. To the extent that international courts approximate this transnational ideal—and we shall see below that a growing number of international courts do so—their behaviour and effects can only be studied in the context of a liberal framework that disaggregates and looks inside individual states.

18  Even with respect to interstate courts, however, liberals have increasingly looked to domestic state-society relations to understand the reasons why, and the conditions under which, states commit to accept the jurisdiction of an international court. Moravcsik (2000) has influentially suggested that certain types of states, and particularly transitional democracies, are particularly likely to accept the jurisdiction of human rights courts in order to ‘lock in’ recent democratic reforms, the broader implication being that states may accept international court jurisdiction, not to bind other states, but rather (or also) to bind themselves and their successors. In a similar vein, Sarah McLaughlin Mitchell and Emilia Justyna Powell (2011) have offered an innovative argument that links varying state acceptance of international court jurisdiction to the nature of states’ domestic legal (common, civil, or Islamic law) tradition, producing systematic differences among the three types of states in their acceptance of ICJ jurisdiction.

19  Finally, insofar as we are interested in whether states comply with international law—and/or with the rulings of international courts—liberal theorists argue that a state’s propensity to comply is likely to vary as a function of domestic (rather than idealized ‘national’) interests, including ‘compliance constituencies’, who favour obedience to international rules, as well as those ‘violation constituencies’, who favour defiance, and the representative institutions that shape the influence of these constituencies (Kahler, 2000; Moravcsik, 2013, 92; Alter 2014, 5–28). Furthermore, in the liberal view, enforcement of international law can take the form of ‘horizontal’ or interstate arrangements, such as state retaliation or loss of international reputation for noncompliance, or they can take a ‘vertical’ form as states ‘internalize’ the commitments of international law, in a given state’s legal, political, or social system (Koh, 1998; Keohane, 1998; Simmons 2009; Moravcsik, 2013, 96–100). To the extent that such vertical enforcement and internalization take place, we are forced once again to disaggregate and look inside the state, an area of strength for liberal IR theory.

20  Despite their substantial differences, realism, institutionalism, and liberalism have evolved as essentially rationalist theories, which assume that actors have fixed, exogenously given preferences, and that each of these actors attempts to maximize their utility subject to the constraints of the domestic and international legal orders. Constructivist theorists, by contrast, proceed from profoundly different core assumptions, arguing that human beings and their preferences ‘do not exist independently from the social environment and its collectively shared systems of meanings (“culture” in a broad sense)’. Instead, ‘[t]he social environment in which we find ourselves, “constitutes” who we are, our identities as social beings’ (Risse, 2004). For constructivist theorists of IR, therefore, the international environment is not simply material but also normative, and international ideas, norms, and rules are expected to ‘constitute’ actors. Actors’ preferences, in other words, are not exogenously given and fixed, as in rationalist models, but endogenous to institutions, and individuals’ identities are shaped and re-shaped by their social environment (Wendt, 1999; Hurd, 2008).

21  Taking this argument to its logical conclusion, constructivists generally reject the rationalist conception of actors as utility-maximizers operating according to a ‘logic of consequentiality’, in favour of March and Olsen’s conception of a ‘logic of appropriateness’. In this view, actors confronting a given situation do not consult a fixed set of preferences and choose their actions in order to maximize their expected utility, but look to their socially constructed roles and ask what sort of behaviour is appropriate in that situation (March and Olsen, 1989, 160–62).

22  In related work, drawing largely on Jürgen Habermas’s theory of communicative action, Thomas Risse (2000) has identified a third potential logic of social action, which he calls the logic of arguing or deliberation. In a logic of arguing, political actors do not simply bargain based on fixed preferences and relative power; they may also question their own beliefs and interests and be open to persuasion and the power of a better argument (Risse, 2000, 7). Risse concedes, however, that genuine argumentative rationality likely exists only under a fairly restrictive set of preconditions, including the existence of a ‘common lifeworld’ among the participants, the presence of uncertainty or imperfect information, and international institutions based on non-hierarchical relations enabling dense interactions in informal, network-like settings (Risse, 2000, 19–20).

23  Although IR constructivists have only recently turned their attention to the study and specific features of international legal norms (Finnemore, 2000), the focus on the norms, and their power to define appropriate behaviour and even ‘constitute’ actors, makes constructivism an appealing theory for many international legal theorists (Brunnée and Toope, 2013). Given the emphasis of constructivist theory on the constitutive power of international norms, it should not be surprising that much of the constructivist literature has focused on the various non-instrumental mechanisms whereby international law may influence states, including Franck’s (1990) concept of ‘compliance pull’ of legitimate legal norms; Brunnée and Toope’s (2010) related conception of ‘interactional international law’ arising out of ongoing practices that generate ‘fidelity to the rule of law’ in international affairs; Harold Koh’s (1998) ‘transnational legal process’ theory of domestic social, political, and legal internalization and obedience; and Goodman and Jinks’s (2004) concept of national ‘acculturation’ to international norms and rules.

24  By contrast with this rich literature on the effects of international laws and norms on states, constructivists have devoted less attention to international adjudication. However, constructivists such as Christian Reus-Smit have demonstrated a greater sensitivity to the nature of law as a distinctive realm ‘characterized by an institutionally autonomous, distinctive discourse that draws on a pre-existing set of norms and practices of justification, and which delegitimizes the raw pursuit of power and self-interest’ (Brunnée and Toope, 2013, 127, summarizing Reus-Smit, 2004, 37–38; see also Kratochwil, 1989; Alter, 2008). Ian Johnstone (2011) has similarly put forward a constructivist account of international legal deliberation, in which legal discourse emerges as a ‘distinctively powerful form of argumentation’, which requires states to engage in ‘justificatory discourse’ before an interpretive community of both state and non-state actors that distinguish good legal arguments from bad or unpersuasive ones. These accounts of international law as a distinctive, and partially autonomous, form of reasoning, discourse, and argumentation are of obvious relevance to the study of international adjudication. Yet, it is striking that constructivist scholars have thus far focused primarily on the emergence and effects of such discourse in inter-state settings, with less attention to the workings of international courts or arbitrators, which represents an obvious next step in the constructivist research programme.

25  In sum, each of the four leading theories of IR ask a particular set of questions about international law and international courts. Each theory directs our attention to specific causal mechanisms: distributive conflict and power for realists; information and institutions for rational-choice institutionalists; domestic politics and law for liberals; and the potentially constitutive power of norms and ideas for constructivists. Each is potentially useful, and the competition among these theories promises to sharpen our understanding of international law and adjudication. It is, nevertheless, worth highlighting two potential dangers of using off-the-shelf IR theories as guides to the study of international adjudication.

26  First, as David Lake (2013) has recently argued, the existence of discrete IR theories and research programmes runs the risk of producing—and indeed, has already arguably produced—an ‘isms’ war, in which the proponents of competing theories engage in gladiatorial combat designed more to shore up their respective theories than to understand and explain specific outcomes in IR. While this is certainly a danger of a theoretically pluralist discipline, a growing number of IR scholars today advocate pragmatic and eclectic theoretical approaches to the problem-driven empirical research that increasingly dominates IL/IR research (Fearon and Wendt, 2002; Katzenstein and Sil, 2008; Dunoff and Pollack, 2013). And indeed, much of the best political science scholarship adopts precisely a ‘tool kit’ approach to competing theories, drawing from each theory concepts and hypotheses suitable to the author’s specific research question.

27  A second danger of the tendency for political science scholars to draw from existing IR theories is that these off-the-shelf theories, designed in most cases for the study of international security, political economy, or international organizations, may be poorly suited to study the specifically legal features of international adjudication, including the need for states to argue their cases in the language of law, the professional norms and practices of the international judiciary and legal community, and the legitimacy that may accrue to international court rulings as authoritative interpretations of international legal agreements. Happily, as we shall see presently, this danger is increasingly averted in contemporary scholarship by the tendency for scholars to engage in interdisciplinary dialogues that integrate the core ideas of traditional IR theories with the specific features of international law and courts.

28  Notwithstanding the potential for IR theory to contribute to the study of ICTs, the subject of international adjudication was largely ignored by IR scholars for most of the twentieth century. It was only after the end of the Cold War, with the proliferation of international courts and the rise of an interdisciplinary, IL/IR approach to the study of international law and courts, that the long neglect by IR scholars of international adjudication came to an end. During this productive era, scholars in the IR and IL/IR traditions made important contributions with respect to at least four significant questions or themes: (1) the design of international adjudication bodies; (2) the behaviour of litigants, which can be either states or non-state actors; (3) judicial behaviour, with an emphasis on judicial independence; and (4) the dynamic evolution of dispute settlement systems over time.

29  First, in keeping with the increasing IR focus on rational design, a handful of scholars have sought systematically to understand and explain the delegation to, and design of, international adjudication bodies. These are some of the most fundamental questions in international politics and international law, given the significant variation in both delegation to international adjudicators, and the design of those adjudicators. With respect to delegation, both IR and IL scholars note the considerable variation in delegation to international courts across issue-areas, ranging from ‘high’ in international trade, investment, human rights, and criminal law, to ‘low’ with respect to both the use of force and the environment (Abbott and others, 2000; Helfer, 2006). Moreover, even within a single issue-area, delegation of adjudicative authority varies dramatically, such that, for example, some human rights agreements (such as the European Convention on Human Rights) have strong courts with individual access, while others (including all of the United Nations human rights treaties) lack any standing court. Furthermore, even among regimes that provide for international adjudicators, the design of those adjudicators varies widely, with ad hoc arbitration in some areas and standing courts in others. Even among international courts, we find a dizzying array of design features, including provisions for the nomination and appointment of judges, their terms of office, the right to dissent, the question of access or standing for non-state actors, the presence or absence of an appellate procedure, the nature of remedies in cases of non-compliance, and many others (Squatrito, 2018). Each of these dimensions in the design of international adjudication represents a collective state choice, calling for explanation.

30  This is not, of course, an entirely new subject, as legal scholars have long devoted significant attention to the statutes and other design features of individual courts such as the ICJ, the ECJ, and the WTO Dispute Settlement Body. In general, however, IR and IL/IR scholarship has sought not only to analyse and critique the design of individual courts and tribunals, but also to classify and explain broad patterns of dispute settlement and design across multiple international dispute settlement systems. For example, the aforementioned ‘legalization’ volume of International Organization provided an influential analytical framework, with its three dimensions of international court design (access, independence, and embeddedness) and its binary distinction between ‘interstate’ and ‘transnational’ courts. As Keohane and others (2000) argued, differences in design matter because they determine how frequently and by whom courts were used, whether those courts provide for the credible and neutral adjudication of disputes, and whether the resulting decisions have immediate effects in the legal orders of their Member States.

31  Karen Alter (2014) makes a related distinction in her landmark book, The New Terrain of International Law, where she distinguishes between traditional international courts and what she calls ‘new-style’ courts, which combine two key elements: compulsory jurisdiction and the ability of non-state actors (international commissions, prosecutors, institutional actors, and private litigants) to initiate litigation. These two features, Alter argues, remove international courts from dependence on states in accepting jurisdiction in a given case, while at the same time depriving states of their gatekeeping power to prevent adverse cases from coming before courts. In the process, she hypothesizes, these new-style courts can empower (ie, provide external resources to) compliance constituencies within states. Falling squarely into the liberal tradition, Alter argues that the rise, and the subsequent diffusion across the world, of new-style courts is driven by a desire by states to bind not only their counterparts but also themselves to values such as free markets, human rights, and the rule of law.

32  Among institutionalist scholars, Barbara Koremenos has taken the lead in theorizing and empirically studying the design of international dispute settlement systems. In a series of papers, and in her magisterial book, The Continent of International Law, Koremenos has set out to map and explain variations in the design of 234 bilateral and multilateral treaties across a variety of issue-areas. Surveying this sample of treaties, she found that slightly less than half (48%) provide for some kind of dispute settlement (including informal consultations, mediation, arbitration, or adjudication), while just 26% provide for arbitration and 24% for adjudication in the event of a dispute. Crucially, and in line with the rational design tradition, Koremenos hypothesizes that states design dispute settlement provisions, systematically and rationally, to solve specific types of cooperation problems, and she finds strong correlations between enforcement and commitment problems among the Member States, on the one hand, and arbitration or adjudication provisions on the other (Koremenos, 2016). This suggests that states design formal dispute settlement procedures only in the face of future incentives to defect. By contrast, other cooperation problems, such as uncertainty about the state of the world or the behaviour of others, show weaker or no correlations with arbitration or adjudication provisions. Overall, Koremenos’s rich data provide a compelling and positive test of rational design hypotheses about the overall design of dispute settlement, as well as about the sharp differences across issue-areas in the respective use of arbitration and adjudication, which are most heavily used in economic and human rights agreements, and least in environment and security.

33  However, rational choice scholars do not have a monopoly on the study of the design of international courts, and the founding of the International Criminal Court (ICC) in particular has given rise to a rich literature inspired alternately by constructivist, institutionalist, and realist interpretations. In an important constructivist contribution, Nicole Deitelhoff (2009) has argued that the design of the ICC—in particular, the decision to create a powerful court with a prosecutor independent of the United Nations Security Council—represents the outcome of a discursive process in which weaker powers were able to persuade more powerful actors and secure the creation of a powerful new criminal court. Beth Simmons and Allison Danner (2010, 227), in an account informed by both liberal and institutionalist theories, focus on the puzzle of why many states have accepted the compulsory jurisdiction of the ICC, arguing that states do so primarily in order ‘to tie their hands to foreswear certain modes of violent conflict’, and that regime type and history of civil war both influence the decision to ratify. Drawing on credible commitment theory, the authors theorize, and find empirical support for the claim, that certain types of regimes (non-democracies with a recent history of civil war, as well as democracies with no such history) are most likely to be willing to bear the sovereignty costs of accepting ICC jurisdiction (Simmons and Danner, 2010, 234–35). Finally, writing in a realist vein, David Bosco (2014) accepts the claim that the negotiators of the Rome Statute created a court that is unusually intrusive upon state sovereignty, remarkably independent in its prosecutions and rulings, and offering no special privileges for the great powers, but he goes on to argue that great powers have sought both to marginalize and to influence the court, which appears to have responded with caution in terms of opening negotiations of their interests.

34  Works such as these have taken a powerful first step, classifying and mapping some of the most important design features of international adjudication, and offering generalizable explanations for state choices. The social-scientific study of the design of international adjudication is nevertheless in its infancy, seeking thus far to explain only very broad variations in design, such as the decision to create or omit dispute settlement provisions from international treaties, or the choice between interstate and transnational, or traditional or new-style courts. By contrast, IR scholars have thus far paid less attention to the more fine-grained design choices that states make about judicial nomination, appointment, and terms of office, as well as non-state access to courts, and the nature of the remedies available to complainants (for an important exception, see Squatrito, 2018, discussed in para 48 below). Doing so will require greater attention to the types of legal design questions that thus far have been the province primarily of legal rather than IR scholars.

35  A second major contribution of IR scholarship, less frequently discussed but of equal interest, has been to problematize, theorize, and study empirically the behaviour of litigants in international adjudication. Simplifying a rich literature, this work can be divided into two major categories, the first focusing on the behaviour of states as litigants before interstate courts, and the second examining the behaviour of non-state litigants before the growing number of transnational courts.

36  With respect to the behaviour of state litigants, political science scholars have only recently turned their attention to understanding the behaviour of states in initiating (or opting not to initiate) litigation. However, as Todd Allee (2004, 3) notes, the ‘decision to sue’ is an important and under-studied question, of interest not only for its own sake but because the cases that actually reach international courts constitute a small and potentially biased subset of the universe of all international legal disputes (see also Davis, 2012, 1–3). Furthermore, in several international adjudicative systems, states have the right to settle their disputes in the shadow of an impending decision, thus granting, or denying, international adjudicators the right to rule on a dispute and to progressively develop international law.

37  Fortunately, recent political science scholarship has begun to address this question systematically, across a number of issue-areas. In one study of international territorial disputes, for example, Allee and Huth hypothesize that states are most likely to refer international disputes to judicial settlement when the domestic ‘audience costs’ of making significant political concessions to an adversary are high. In such settings, they argue, international judicial rulings can provide political cover for domestically unpopular decisions. Their analysis of nearly 1,500 territorial disputes provides support for the claim that ‘state leaders opt for legal dispute resolution when they are highly accountable to domestic political opposition, as well as when the dispute is highly salient to domestic audiences’ (Allee and Huth, 2006, 219). This study supports the liberal theoretical view that state behaviour with respect to international litigation is driven in large part by domestic as well as international considerations.

38  Christina Davis (2012, 2), in a major study of interstate litigation in the WTO trade regime, offers a similar argument, suggesting that international litigation is particularly useful for democratically accountable governments as a means of responding to domestic pressure and signalling to domestic industries that the government supports their demands:

Engaging in political theater by initiating legal action against a foreign government proves to be an effective strategy not only for dealing with foreign governments but also for managing domestic pressure. Willingness to bear the costs of going to court signals that the government gives priority to enforcement. As a result, incentives to use courts arise from their usefulness as a political tool and not only from their role to interpret the law and allocate punishment.

39  Other work on state behaviour in WTO dispute settlement points to additional influences on state litigation choices, including state power (Sattler and Bernauer, 2011; Klein, 2014), estimates of the probability of winning (Allee, 2004), previous litigation experience (Davis and Bermeo, 2009), concerns about setting useful precedents in various legal fora (Busch, 2007), and the concentrated or diffuse impact of the violation in question (Johns and Pelc, 2018). Still other work has explored the conditions under which states join WTO litigation as third parties (Busch and Reinhardt, 2008; Johns and Pelc, 2014, 2016), and agree to settle disputes prior to a judicial ruling (Busch, 2000; Busch and Reinhardt, 2000/2001; and Guzman and Simmons, 2002).

40  Given the rise of transnational or new-style courts, no account of litigant behaviour is complete without a discussion of the behaviour of individual, non-state litigants. Traditionally, individuals and other non-state actors enjoyed no direct access to international adjudication systems, and relied on their own national governments to espouse (or, more frequently, not espouse) their claims under international law (Espousal of Claims). Today, however, non-state actors enjoy the opportunity to initiate litigation through a variety of avenues at new-style or high-access courts:

• •  Individuals may initiate complaints before international adjudicators against their own states for human rights violations, as in the European Court of Human Rights (ECtHR) (where all States Parties must accept the individual right to petition), the Inter-American Court of Human Rights (IACtHR) (where States Parties may accept such an individual right), and the committees established to hear petitions under the various UN human rights treaties (where States Parties can, although only a fraction do, agree to optional protocols allowing such petitions) (Klein, 2014) (Human Rights, Treaty Bodies).

• •  Individuals in some international regimes can initiate legislation in national courts, which then consult international courts under a preliminary reference mechanism, most notably in the EU but also in other legal settings such as the Andean Community (Alter, 2001; Alter and Helfer, 2017) (Prejudgment Interpretation: Court of Justice of the Andean Community of Nations).

• •  Private investors may also initiate binding arbitration proceedings against states in investor-state arbitration disputes, as under the North American Free-Trade Agreement and the more than 3,000 existing bilateral investment treaties (for important IR-influenced contributions on investment arbitration, see eg Simmons, 2014; Poulsen, 2015; Wellhausen, 2016; Bonnitcha and others, 2017; Pelc, 2017; St John, 2018; and Langford and others, 2019) (International Investment Arbitration).

41  In addition to these various legal avenues through which they can initiate litigation, non-state actors in some interstate adjudication systems enjoy the limited right to submit amicus curiae briefs, a practice which has been employed most strikingly, and controversially, in the WTO dispute settlement system (Klein, 2014) (Amicus Curiae: Dispute Settlement System of the World Trade Organization (WTO)). Finally, with the dramatic increase in international criminal courts and tribunals, individual actors may also find themselves as defendants in international criminal proceedings, a recent and dramatic development in the history of international adjudication (Bass, 2000; Bosco, 2014).

42  IR scholars have waded selectively into this question of non-state litigant behaviour, focusing most of their early attention on patterns of litigation in the EU’s preliminary reference procedure, where they have problematized both the behaviour of litigants in bringing cases to their national courts, as well as the relationship between national courts and the ECJ. With respect to individual litigants, both political scientists and lawyers have examined systematic differences in the behaviour of ‘one-shot’ and ‘repeat players’ in EU litigation (Conant, 2002), and in particular the importance of well-financed corporate litigants (Rawlings, 1993), as well as state-subsidized groups such as women claiming gender discrimination (Alter and Vargas, 2000; Caporaso and Jupille, 2001), in bringing important test cases and shaping the development of EU law. At the broadest level, Stone Sweet and Brunell (1998) find that individual litigants under the preliminary reference procedure are most likely to target regulations adopted by states representing substantial economic markets, which they interpret as evidence in favour of a neo-functionalist account of European integration.

43  However, the question of whether, when, and why national courts submit questions for preliminary rulings to the ECJ, and also whether and why those national courts accept the direct effect of those decisions and the supremacy of EU law over national law, is just as important as individuals claiming their rights under EU law. Within the political science literature, responses to these questions fall into three broad camps: the neo-functionalist ‘judicial empowerment view’, a related ‘inter-court competition’ model, and a ‘sustained resistance’ view (Pollack, 2013a). In the neo-functionalist view, the willingness of national courts to accept ECJ jurisdiction and jurisprudence can be explained in terms of the extent to which ECJ rulings ‘empowered’ national courts within their own domestic political and legal systems (Burley and Mattli, 1993; Weiler, 1994). In a variant of this approach, Karen Alter’s (2001) inter-court competition account demonstrated that the preliminary reference procedure was accepted most readily and used most ambitiously by lower courts, whose judges stood to gain from a direct relationship with the ECJ. By contrast, national high courts in key countries such as France and Germany, notwithstanding their legal obligation to refer questions of EU law to the ECJ, often proved reluctant to do so, and in some instances even attempted to quash lower-court references to the ECJ. Over time, however, ECJ doctrine filtered into the national legal orders through lower-court decisions, and high courts were reluctantly forced to accept the doctrines and the authority of the ECJ. Third, and finally, we see the emergence over the past two decades of a ‘sustained resistance’ view, in which national courts persistently resist either sending preliminary references to Luxembourg, or else attempt to ‘contain’ the effects of ECJ decisions in the domestic legal order (see eg Golub, 1996; Alter, 2000; Conant, 2002; Wind and others, 2010; Wind, 2016; for a pioneering study of national-court resistance to the Inter-American Court of Human Rights, see Huneeus, 2011). In all of these ways, the ECJ’s relationship with national courts, typically depicted as a vital resource for the Court in its conflicts with Member governments, also serves as a constraint, limiting the Court’s ability to impose unwelcome judicial doctrines on reluctant national judges.

44  Notwithstanding these impressive advances in the study of EU litigation, the systematic study of individual litigation before other international adjudicative bodies remains in its infancy. By contrast with the large EU literature, we know relatively little about the determinants of individual litigation in other transnational courts (but see Alter and Helfer, 2017 on the Andean Tribunal), and IR scholars have also largely ignored the admittedly low levels of individual activity before UN human rights committees (Klein, 2014).

45  A large and well-developed third strand of IR and judicial-politics scholarship has focused on explaining the nature, extent, and determinants of international judicial behaviour, with an emphasis on the related question of judicial independence (Independence: International Adjudication). The focus in this literature has been on characterizing and explaining the voting behaviour of international judges, often with an eye to establishing the extent and the determinants of their independence from the states that appoint them to their positions, and to other external, extra-legal influences on their behaviour (Ginsburg, 2013; Voeten, 2013). While a few legal studies had previously problematized and studied the independence of specific international courts (eg Weiss, 1987), political science scholarship over the past two decades has systematized such analysis, defining judicial independence as ‘the set of institutional and other factors that to a lesser or greater extent allows judges autonomy from the preferences of other political actors when these judges issue legal opinions’ (Voeten, 2013, 421–22), and providing comprehensive theoretical frameworks to identify a wide range of potential control mechanisms available to states, as well as other sources of extra-legal influence over international judicial behaviour.

46  IR theorists have long debated the extent and the sources of international judicial independence. At one extreme, realists suggest that international judges must constantly anticipate the reactions of the great powers to their rulings and obfuscate their legal rulings accordingly. At the other extreme lie ‘trusteeship’ scholars, who argue that international judicial independence is virtually complete because states enjoy few or no control mechanisms with which they can influence the international judiciary. In the formulation of Karen Alter (2008, 47), ‘the venue and deliberative style in which interpretive politics takes place is very different from the negotiating table dominated by state actors. Courtroom politics take place in an environment highly constrained by law and legal procedure, where judges have a privileged position because they get to ask the questions, decide what is and is not relevant, and determine the outcome’. Under such conditions, Alter (2008, 44) argues, efforts by Member State principals to influence international courts will be channelled away from control mechanisms and toward either ‘rhetorical politics’, in which actors attempt to persuade judges in the language of the law, or ‘legitimacy politics’, in which actors attempt to influence the public perception of the legitimacy of a court’s decision, or indeed of the court itself.

47  Between these two extremes lies a third approach, informed by principal-agent analyses in economics and political science, which theorizes international courts as agents, created by collective principals and ultimately accountable to those principals, yet pursuing their own preferences within the broad and imperfect constraints imposed by Member State control mechanisms (Pollack, 2003; Helfer, 2006; Ginsburg, 2013) (Political Theory of International Adjudication). Helfer (2006), in an important and influential contribution, elegantly synthesizes a range of principal-agent analyses, arguing that any theory of a given international tribunal’s ‘constrained independence’ or ‘strategic space’ must incorporate both the full array of specific control mechanisms anticipated by principal-agent analysis (which he usefully divides into ex ante and ex post mechanisms, which can be used by states either individually or collectively) and the ‘global community of law’, which he defines as ‘discursive constraints (eg procedural rules, interpretive methodologies, and substantive norms) generated by interactions among participants in the global community of law and internalized by tribunal members’. In so doing, Helfer holds out the promise of a genuinely interdisciplinary and synthetic account of international judicial independence, which takes into account both the panoply of principal-agent control mechanisms available to states, as well as the broader and more diffuse influence of a global community of law.

48  Controversies remain within this literature, but the focus of analysis has increasingly moved from broad, binary questions of whether international courts are entirely obedient great-power servants or entirely independent trustees, to more fine-grained analyses of the design and effectiveness of specific control mechanisms, such as judicial appointment and reappointment practices, legislative overruling, and the prospect of state noncompliance (Helfer, 2006; Voeten, 2009). On the design side, Theresa Squatrito (2008) has undertaken a systematic study of the formal independence (as opposed to the informal or behavioural independence) of 24 standing international courts. Squatrito identifies eight statutory design elements that may act as safeguards of judicial independence—including selection and tenure, eligibility criteria, resources, rules of procedure, recusal and activities incompatible with judicial office, confidentiality of deliberation, oath of office, and privileges and immunities—for each court in her sample. Her findings demonstrate that international courts vary dramatically in their formal independence, with judges in certain courts enjoying substantially greater formal safeguards of their independence than others, and she finds that much of the variation across courts is driven by substantial differences in the selection and tenure of judges. Squatrito’s study is significant both for the fine-grained nature of her measurement of international-court design choices, and as the first step towards studying the possible influence of formal independence (in terms of design) on informal behaviour (in terms of judicial behaviour).

49  Echoing Squatrito’s focus on judicial selection and tenure, a number of IR scholars (Voeten, 2009; Elsig and Pollack, 2014) have turned their attention to the rules and processes governing judicial selection, demonstrating that states tend to nominate and appoint judges whose preferences match their own (Voeten, 2009), and that appointment processes at courts like the ICJ and the WTO Appellate Body have become increasingly politicized over time (Elsig and Pollack, 2014; Creamer and Godzimirska, 2017; Shaffer, 2018) (Election of Judges: International Court of Justice (ICJ); Election of Appellate Body Members: World Trade Organization (WTO)), providing Member States with an opportunity to shape the preferences of the judiciary, as well as put pressure on judges with renewable mandates. Dunoff and Pollack (2017) have focused more narrowly on the question of renewable terms of office, a design feature that they argue interacts with another design feature, the possibility of individual opinions or dissents, to influence the independence of judges vis-à-vis national governments (Separate Opinions).

50  Moving from formal or design features to behavioural independence in practice, IR and IL/IR scholars have pursued an active research agenda examining the nature and sources of judicial independence in the ECtHR (Voeten, 2008), the ICJ (Posner and Figueiredo, 2005), and among WTO panels and the Appellate Body (Busch, 2000, 2007; Busch and Reinhardt, 2000/2001, 2006; Busch and Pelc, 2010; and Davis 2012), among others. The full range of this debate, however, can best be observed in the vibrant literature on the independence of the Court of Justice of the EU (‘CJEU’), where we see all three of the aforementioned theories vying for empirical validation. First, echoing the views of the realists, a group of ‘intergovernmentalist’ scholars have argued that the Court, as the creation of the EU’s member governments, is bound to follow the wishes of the most powerful Member States. These Member States, Geoffrey Garrett argued in a series of articles, established the ECJ as a means to solve problems of incomplete contracting and monitoring compliance with EU obligations, and they rationally accepted ECJ jurisprudence, even when rulings went against them, because of their longer-term interest in the enforcement of EU law (Garrett, 1992, 1995). In such a setting, the ECJ might identify ‘constructed focal points’ among multiple equilibrium outcomes, but the Court is unlikely to rule against the preferences of powerful EU Member States (Garrett and Weingast, 1993, 189).

51  In response to these intergovernmentalist claims, a second school of thought, closer to the trusteeship account, argued that the Court, as a legal body, is profoundly independent and largely unconstrained by EU member governments, which have generally been reduced to largely ineffective reactions against the Court’s activist and integrationist legal rulings (Judicial Activism). In their neo-functionalist account of European legal integration, for example, Anne-Marie Burley and Walter Mattli (1993) argued that the Court’s language of the law acted as both a ‘mask’ for the policy implications of the Court’s doctrinal interventions, which were not immediately evident to the Member States, and as a ‘shield’ against political attacks. In this view, carried forward in later scholarship by Weiler (1994), Mattli and Slaughter (1998), Alter (2001), and Stone Sweet and Brunell (1998), ‘the move to supremacy and direct effect must be understood as audacious acts of agency’ by the Court (Stone Sweet and Caporaso, 1998, 129). In perhaps the most compelling extension of the trusteeship argument, Stone Sweet and Brunell (2013) provide a sharper and more discriminating definition of a ‘trustee court’, which in their view must be: (1) the authoritative interpreter of a given regime’s law, (2) enjoying compulsory jurisdiction, and (3) difficult or impossible for the contracting states to overrule when interpreting treaty law. Certain international courts, they suggest, meet these criteria, including the CJEU, the ECtHR, and the WTO Appellate Body. Such trustee courts, they argue, are in a particularly strong position vis-à-vis their Member States, and their judges use this discretion to engage in ‘majoritarian activism’, tending to rule against states whose positions are out of synch with a majority of other state-parties. In so doing, they argue, trustee courts act, in effect, as agents of the majority, allowing them to achieve outcomes that would otherwise be impossible under consensus-based decision-making rules, and helping to drive the process of legal integration in their respective regimes.

52  In recent years, a third school of thought, informed largely by principal-agent approaches, has taken up a position between the ‘court as obedient servant’ and the ‘court as trustee’ positions, suggesting that, while the CJEU enjoys substantial discretion vis-à-vis the member governments, that discretion is bounded by the threats of Member State noncompliance and legislative overrule. In their 2015 book, Cliff Carrubba and Matthew Gabel propose and test a rational-choice theory of international judicial behaviour. Like other principal-agent theorists, they argue that international courts can help promote compliance with agreements, acting as both a ‘fire alarm’ for the identification of potential violations and as an ‘information clearinghouse’ through litigants and Member States can weigh in on disputes (Carrubba and Gabel, 2015, 24). Courts, in this model, are assumed to be strategic actors with independent preferences, seeking wider application of international rules while avoiding noncompliance with their rulings (Carrubba and Gabel, 2015, 38). From this model, the authors derive and test a Political Sensitivity Hypothesis on a dataset of 40 years of CJEU rulings, predicating that strategic judges are likely to be sensitive to the signals from Member State observations and rule accordingly. Controlling for a variety of other factors such as the position of the European Commission and the Opinion of the Advocate-General in the case, the authors produce robust findings showing a strong correlation between Member State observations and Court rulings, providing the most compelling evidence to date of a strategic Court tailoring its rulings to the expressed preferences and anticipated responses of the Union’s Member governments.

53  Writing in a similar vein, Olof Larsson and Daniel Naurin (2016) undertake a sophisticated test of the override thesis, finding not only that Member State observations correlate with CJEU rulings, but that the impact of Member State positions is greater in those cases where the ruling can be overturned by a qualified majority (as opposed to a unanimous) decision of the Member States. This finding suggests that judges are attentive not only to cues about national preferences, but also to the decision-making rules that make override more or less difficult. In a related work, Larsson and others (2017) find that, controlling for other factors, the CJEU engages in greater citation to past decisions in cases that are contested by the EU’s Member States, suggesting that the Court may seek to legitimize controversial rulings through more intensive appeal to precedent (Judicial Precedent). These studies, and others like them (eg Stone Sweet and Brunell 2013), suggest that the Court is indeed a strategic actor, enjoying a large but not unbounded area of discretion, and selectively responsive to political cues about the acceptability of its decisions.

54  Fourth and finally, IR scholars have begun to develop and test hypotheses on the conditions under which, and the ways in which, international dispute settlement systems develop dynamically over time. Drawing from historical institutionalist theories, these scholars suggest that judicial decisions, and the responses to those decisions by litigants, can create ‘feedback effects’ that influence the further development of both the law and the adjudication system (Pierson, 2000; Greif and Laitin, 2004; Fioretos and others, 2016). Oversimplifying only slightly, some of these accounts emphasize positive feedbacks, whereby judicial decisions generate a virtuous cycle of further litigation, development of law, and support for the system; or negative feedbacks, whereby judicial decisions create a vicious cycle of opposition among governments, domestic courts, litigants, or public opinion, and thus sow ‘the seeds of their own demise’ (Greif and Laitin, 2004, 634).

55  With respect to positive feedbacks and virtuous cycles, IL/IR scholars have suggested that transnational dispute settlement systems, characterized by high levels of access, independence, and embeddedness, should show greater dynamism over time, as individuals (not subject to governmental gatekeeping) bring cases that are likely to be decided independently and then enforced through domestic legal systems, creating a feedback loop of ever more developed law and ever-growing caseloads (Keohane and others, 2000). The two most striking examples of vibrant, dynamic transnational courts in the literature are the ECJ and the ECtHR, both of which have seized upon an initial trickle of claims from individual litigants to create legally enforceable rights under international law, which have in turn provided incentives for further litigation in a virtuous circle of ever-greater legal integration (Helfer and Slaughter, 1997; Stone Sweet and Brunell, 1998; and Alter, 2001). Indeed, Moravcsik (2013) suggests that the explanation of dynamic development of dispute settlement regimes is one of the signature contributions of liberal theory to the study of international law, and positive feedbacks can help to explain what legal scholars would call the progressive development of international law. By contrast, IR scholars see interstate courts such as the ICJ as less promising venues for such positive feedbacks (Posner and de Figueiredo, 2005), but the possibility of such effects is illustrated by the rapid growth and development of the WTO Dispute Settlement Body, which adjudicated a steady stream of hundreds of cases and dozens of appellate decisions in its first several decades, developing a substantial body of law, a de facto practice of precedent, and arguably greater trade liberalization than the WTO’s formal trade negotiations (Goldstein and Steinberg, 2009; Pelc, 2012).

56  By the same token, however, a growing number of scholars have argued—in various theoretical registers—that the workings of international adjudication systems have produced negative feedbacks and self-undermining dynamics over time. In a pioneering early study, Laurence Helfer (2002, 1854) theorized what he called the process of ‘overlegalization’, which ‘exists where a treaty’s augmented legalization levels require more extensive changes to national laws and practices than was the case when the state first ratified the treaty, generating domestic opposition to compliance or pressure to revise or exit from the treaty’. In addition to theorizing the concept, Helfer provided case studies from the area of human rights law, in which three Caribbean states had exercised their option to withdraw from agreements that had resulted in judicial constraints that went beyond states’ original expectations and imposed domestic costs that outweighed the reputational costs of departure (see also Helfer, 2005 and 2013 on exit). Since Helfer’s study, other scholars have moved to empirically catalogue and theoretically grapple with the possible negative feedbacks from the workings of ICTs. Leslie Johns (2015), for example, has argued that strong international courts provide the benefit of promoting compliance with international law, but they do so at the expense of discouraging negotiated settlements and undermining the stability of international agreements and encouraging withdrawal from international regimes or from the dispute settlement provisions of those regimes.

57  In recent years, we have witnessed the explosion of a substantial new body of research, which we might call backlash studies, focusing on theorizing and empirically studying the ever-growing (through also highly variable) phenomenon of resistance to ICTs. In their introduction to a recent symposium on resistance to international courts, Madsen and others (2018) offer a useful framework for theorizing such resistance (albeit one drawing more from sociology than from IR theory) distinguishing ‘between mere pushback from individual Member States or other actors, seeking to influence the future direction of an IC’s case-law and actual backlash in terms of critique triggering significant institutional reform or even the dismantling of tribunals, the latter typically involving the collective action of Member States’ (Madsen and others, 2018, 198; emphasis in original; for similar typologies, see Sandholtz and others, 2018, 160; Alter and Zürn, 2019) (Sociological Approaches to International Adjudication). Focusing on backlash, the authors suggest that it should be considered as a ‘reaction to a development … with the goal of reversing that development’. Developing a four-stage framework, they examine in turn: (1) the actors, or coalitions of actors, who press for backlash, ranging from state governments to members of the legal community, national courts, politicians, and civil society at large; (2) the many forms of resistance, including inter alia engaging in delegitimizing public critique, withdrawing from jurisdiction, restricting access to the court, failing to cooperate, systematic noncompliance, cutting budgets, altering institutional rules or mandates, blocking judicial nominations to paralyze the court, or eliminating the court altogether (Madsen and others, 2018, 213); (3) the ‘resilience techniques’ employed by international courts and judges to either pre-empt ex ante or mitigate ex post the effects of backlash effects (Madsen and others, 2018, 214); and finally (4) the outcomes of backlash events, which can range anywhere from having no effect to closing down the court.

58  Although the Madsen and others framework has been highlighted here, backlash studies have produced other systematic, cross-court frameworks (Pauwelyn and Hamilton, 2018; Sandholtz and others, 2018; Voeten, 2018) as well as a spate of excellent court-specific studies addressing backlash with respect to African courts (de Wet, 2013; Gathii, 2014; Alter and others, 2016; Daly and Wiebusch, 2018); EU courts (Alter, 2000; Davies, 2012; Dyevre, 2016; Blauberger and others, 2018; Hoffmann, 2018); human rights courts (Helfer, 2018; Sandholtz and others, 2018); the ECtHR (Cali and others, 2013; Madsen, 2015, 2017; Stiansen and Voeten, 2018); the IACtHR (Huneeus, 2011; Soley and Steininger, 2018; Contesse, 2019); international criminal courts (Clarke and others, 2016; Vinjamuri, 2016; Mills and Bloomfield, 2017; Rossi, 2018; Lovat, 2020); regional integration courts (Caserta and Cebulak, 2018); the WTO Dispute Settlement Body (Creamer and Godzimirska, 2016; Shaffer and others, 2016; Shaffer, 2018; Creamer, 2019); and investor-state dispute settlement (Roberts, 2017a, 2017b; Lanford and Behn, 2018; Roberts and St John, 2019).

59  Studies of backlash against ICTs draw from a variety of IR and other theoretical frameworks, including realist and institutionalist theories that attempt to identify the limits of Member State control over international courts. However, liberal IR scholarship has arguably made the most distinctive IR contribution to backlash studies by exploring the relationship between domestic political developments, including the rise of populism, and backlashes against international law and organizations (Posner, 2017; Copelovich and Pevehouse, 2018). For example, in their analysis of backlashes against international human rights and criminal courts, Sandholtz and others (2018) argue that national governments tend to resist the decisions of human rights courts that harm their domestic political interests (rather than the interests of the state as a whole) by reducing public support for the government or strengthening regime opponents. They argue that backlash is more likely when these ‘regime costs’ of international court decisions rise. In another recent paper, Erik Voeten (2018) similarly links the origins of backlash to domestic politics, focusing specifically on the role of populist mobilization to explain the conditions under which states will challenge the authority of an international court or tribunal. According to Voeten’s theory, states are most likely to engage in backlash against courts (international and domestic) whose rulings provide protections to groups (such as migrants, prisoners, or other minorities) that are the target of domestic populist mobilization. By ruling in favour of such groups, he argues, international courts can ‘provide kindling to burning populist fires’, prompting governments to react strongly against them. Moreover, as an ideology, populism provides a powerful set of claims against international courts, which are both countermajoritarian institutions, and foreign institutions, set against ‘the will of the people’ (Voeten, 2018, 2). In empirical terms, Voeten catalogues 28 instances of state backlash against international courts, of which he finds fully 18 were undertaken by populist governments; still others (such as the United Kingdom campaign against the ECtHR) were undertaken by non-populist governments but consistent with the logic of the theory. These studies, and others like them, suggest that any effort to understand the origins and outcomes of backlash against international courts must take into account not only the relationships between states and courts (as in both realist and institutionalist theories) but also how international law and courts interact with domestic law and politics, an area of strength for liberal IR theory.

60  Among international law scholars, IR theory has often enjoyed a bad reputation, narrowly associated with realism and associated with claims that international law and courts play no role—or perhaps even a negative role—in international politics (Koskenniemi, 2001, 2009; Klabbers, 2009). I have argued elsewhere (Pollack, 2013b) that these criticisms are misplaced, since they depict a monolithic IR field in place of the theoretical diversity that characterizes IR scholarship today. We have seen above in section B of this entry that contemporary IR theories (the four ‘mainstream’ approaches examined here) are remarkably diverse in terms of both their assumptions about and their insights into international law, and that they generate unique, value-added contributions to our understanding of ICTs as well. Indeed, as we have seen in section C, IR theories offer important insights into multiple aspects of international adjudication, from the design of ICTs, to the identities and strategies of litigants, the behaviour and independence of international judges, and the development of ICTs over time. Perhaps most promisingly, the application of IR theories to international adjudication is increasingly an interdisciplinary activity, in which legal and political science scholars work together to adopt and adapt IR theory in order to answer fundamental questions about the workings of ICTs and their roles in the international legal order and in world politics.

61  This entry draws in part from, and updates, material first explored in Pollack, 2014. My thanks to the Editor and to two anonymous reviewers for excellent comments and suggestions. I owe a great intellectual debt to Jeff Dunoff, with whom I have explored many of the ideas in this entry, but responsibility for any errors or omissions remains strictly my own.

Mark A Pollack