1. Abstract Instruments of General Application
(a) Legislative-Type Instruments: The EU and the United Nations Security Council
6 International organizations adopt instruments of secondary legislation, understood as abstract rules of general application that become binding law per se without need or room for consent or ratification. The addressees of such legislation will usually be States. But it can also reach into the internal legal orders of States and directly confer rights and duties on individuals.
7 A prominent example is the EU, which has extensive powers to adopt secondary legislation in the form of so-called regulations and directives. While the former is binding in its entirety and directly applicable in the Member States (Art. 288 (2) Treaty on the Functioning of the European Union, [(signed 13 December 2007, entered into force 1 December 2009) (2008) OJ C115/1]; ‘TFEU’), the latter is binding as to the result to be achieved only (Art. 288 (2) TFEU). Individual treaty provisions provide the EU with defined powers and determine the procedure to be followed, which is now mostly the co-decision procedure requiring the Council of Ministers (through qualified majority voting) and the European Parliament to act in agreement. The parallel with domestic systems of legislation has been pushed even further by the Lisbon Treaty which provides for an ‘ordinary legislative procedure’ (Art. 294 TFEU).
8 Since the 1990s the UN Security Council has developed the practice of passing resolutions of a legislative-type structure. These resolutions set forth general provisions addressed to all Member States which need to take implementing action on which they report to a monitoring committee of the Security Council. The competence of the Council for such resolutions lies in Chapter VII, Arts 39 and 41 UN Charter, and possibly Art. 25 UN Charter. Art. 41 UN Charter empowers the Security Council to take any non-forcible measures it deems fit to maintain international security and world peace, including legislative-type action.
9 Such legislative-type resolutions have been passed by the Security Council in matters ranging from anti-terrorism (UNSC Res 1373  [28 September 2001]) to non-proliferation of weapons of mass destruction (UNSC Res 1540  [28 April 2004]).
10 This practice of the Security Council has received some criticism as being ultra vires or an abrogation of the treaty-making power pertaining to the Member States. However, the practice of the Security Council is arguably within its powers under Chapter VII UN Charter, and the UN Charter does not recognize any reserved competences for Member States other than Art. 2 (7) UN Charter which exempts Chapter VII powers of the Security Council.
(b) Tacit Consent Procedures
11 International organizations that are UN agencies are regularly able to amend technical and other regulations of the treaties negotiated under their auspices or even the constitutive treaty to keep pace with the rapidly-evolving technology (tacit amendment; see also Treaties, Amendment and Revision). This means that the organization’s organ which adopts the amendment at the same time fixes a time period within which States Parties will have the opportunity to notify either their acceptance or their rejection of the amendment, or to remain silent on the subject. In case of silence, the amendment is legally considered to have been accepted by the party, unless the party has stated that its express approval is necessary. These amendments thus become binding on Member States without a further act of ratification or acceptance being required. Such regulatory authority need not be included in the constitutive treaty but may be conferred on the international organization by an implementing treaty or by decision of the organization’s plenary body.
12 Examples of such tacit amendments, effectively requiring States to opt out rather than to opt in as would be consistent with State consent, are the procedures of the IMO (eg Art. 16 International Convention for the Prevention of Pollution from Ships [(signed 2 November 1973, entered into force 2 October 1983) 1340 UNTS 184; ‘MARPOL Convention’]; Art. 8 International Convention for the Safety of Life at Sea, 1974 [(concluded 1 November 1974, entered into force 25 May 1980) 1184 UNTS 2]); the International Telecommunications Union (‘ITU’; Art. 54 Constitution and Convention of the International Telecommunication Union [(concluded 22 December 1992, entered into force 1 July 1994) 1825 UNTS 143]); the International Civil Aviation Organization (ICAO) (Art. 90 Convention on International Civil Aviation [(signed 7 December 1944, entered into force 4 April 1947) 15 UNTS 295]; ‘Chicago Convention’); the World Meteorological Organization (WMO) (Art. 28 Convention of the World Meteorological Organization [done 11 October 1947, entered into force 23 March 1950 1434 UNTS 3]); and the World Health Organization (WHO) (Arts. 21–2 Constitution of the World Health Organization [(signed 22 July 1946, entered into force 7 April 1948) 14 UNTS 185], Art. 59 World Health Organization ‘International Health Regulations’ [(adopted 23 May 2005, entered into force 15 June 2007) WHA58.3]); and also of regional fisheries organizations (Art. 12 North-East Atlantic Fisheries Convention [with Annex] [(signed 24 January 1959, entered into force 27 June 1963) 486 UNTS 157]). Similarly, the International Atomic Energy Agency (IAEA) may adopt safety standards that become binding in all operations in which the IAEA participates (Arts 3, 12 Statute of the International Atomic Energy Agency [(done 26 October 1956, entered into force 29 July 1957) 276 UNTS 4]). In the case of the ICAO, amendments (annexes) adopted by 2/3 majority in the Council become binding on all contracting States unless a majority of them registers their disapproval.
(c) Administrative Rule-Making
13 A sub-category of abstract instruments comprises what may be labelled administrative rule-making. In contradistinction from secondary legislation such rule-making is not addressed to States or individuals in general, but governs an international organization’s administration of a given matter.
14 An example of such rule-making is provided by the International Seabed Authority (ISA) administering the exploration and exploitation of the mineral resources of the deep seabed pursuant to its regulations (Arts 160, 158 UN Convention on the Law of the Sea [done 10 December 1982, entered into force 16 November 1994] 1834 UNTS 397). Furthermore, the practice of international territorial administration developed by the UN in instances such as Kosovo and East Timor involves much rule-making applicable across the administered territory.
(e) Decision-Making Procedures
18 The procedure to be followed by the international organization in adopting any of the above normative instruments may variously call for unanimity, consensus, or different types of majority voting and qualified majority voting, meaning not just a simple or absolute majority but the stipulation of a quorum and the weighting of members’ votes in accordance with the functions of the international organization. Art. 27 (3) UN Charter according to which decisions of the UN Security Council on non-procedural matters are to be made by affirmative vote of nine members, including the concurring votes of the permanent members, is a well-known example of such qualified majority voting (for further examples see Sands and Klein 275–81).
19 There is also decision-making on normative instruments by limited membership bodies (eg ICAO Council, ISA Council); representation in these bodies will be based on the principles of: a) equitable geographical distribution, b) interests affected in the case of the UN specialized agencies and ISA, and c) weighting of the votes of Member States in the case of economic organizations.
20 The combination of majority voting and decision-making by limited membership bodies comes close to meeting a comprehensive concept of legislation, referring to abstract norms of general application, susceptible of repeated application, which may be adopted by majority vote but become binding on the minority (International Organizations or Institutions, Decision-Making Process; see also International Organizations or Institutions, Decision-Making Bodies).
2. Administrative Decisions
21 International organizations also develop international law through their power to take administrative-type action, applying law in specific instances. The authority vested in international organizations to take administrative decisions varies widely in form and legal effect.
22 The most elaborate examples are the EU Commission’s power to adopt binding decisions (Art. 288 (4) TFEU) to administer, inter alia, the areas of competition and State aid (see also European Administrative Law), and the International Seabed Authority’s power to administer the deep seabed through binding decisions (Art. 162 UNCLOS).
3. Contractual-Type Arrangements
23 Contractual-type arrangements entered into by international organizations and States consistent with the international organizations’ mandates further develop international law in two respects. They will not only create specific contractual-type rights and obligations for the parties to the arrangement, but they will also often reference instruments and policies thus conferring legal authority on them.
24 The World Bank is a leading exponent of this practice, in concluding legally binding loan agreements with borrowers (the recipient State) under international law registered with the UN, which include the Bank’s policies and sometimes also external instruments.
4. Judicial and Quasi-Judicial Pronouncements
25 Increasingly, international organizations provide courts or tribunals with compulsory jurisdiction over disputes between the organization and its Member States, its staff, or even individuals, and sometimes also over disputes between Member States (Administrative Boards, Commissions and Tribunals in International Organizations). Organizationally, such courts or tribunals may be either attached to an existing international organization or be set up as a separate international organization. Similar dispute resolution functions may be exercised by internal oversight bodies that are institutionally shielded from the international organization.
26 In accordance with their compulsory jurisdiction, the courts and tribunals hand down judicial decisions that become binding on the parties to the dispute without their consent.
27 The legal precedent effect of such pronouncements regularly transcends the dispute at issue, raising the spectre of the relationship with the International Court of Justice (ICJ) and its universal but not compulsory jurisdiction.
28 Examples are the EU court system that has all the heads of jurisdiction mentioned, the International Tribunal for the Law of the Sea (ITLOS) (which is an international organization) with jurisdiction over disputes, the International Seabed Authority and individual operators, and between States parties to the UN Convention on the Law of the Sea, the UN Staff Tribunal with jurisdiction over disputes with staff, the World Trade Organization (WTO) Panels and Appellate Body (regardless of whether they can be classified as courts in the full sense) with jurisdiction over disputes between member States, the World Bank’s International Centre for Settlement of Investment Disputes (ICSID) with jurisdiction over disputes between parties to the Centre’s foundational treaty, and the World Bank’s Inspection Panel with administrative review jurisdiction over disputes between the Bank and affected individuals.
29 In addition, there are quasi-judicial pronouncements made by specialized organs of international organizations in the course of controlling compliance with and enforcing obligations of Member States under the constitutive instrument, an example of which is the UN Human Rights Council.
5. International Institutional Law
30 From international organizations’ constitutive instruments and the internal and external secondary international law developed through the practice of international organizations, a ‘general part’ of the law of international organizations (also international institutional law or international administrative law) can be analytically deduced. The function of this body of principles and rules is to ensure that (legal) rationality is observed in the exercise of international law-development powers by international organizations. It covers, inter alia, a typology of legal instruments, procedures, legality requirements, enforcement, and judicial review. It is applicable to all or almost all subject-matter-specific international law developed by international organizations.