This textbook provides a detailed and comprehensive overview of the international legal framework applicable to the movement of persons across borders. The role of international law in this field is complex, and often ambiguous: there is no single source for the international law governing migration. The current framework is scattered throughout a wide array of rules belonging to numerous fields of international law, including refugee law, human rights law, humanitarian law, labour law, trade law, maritime law, criminal law, and consular law. This textbook cuts through this complexity by clearly demonstrating what the current international law is, and assessing how it operates. The book offers a unique and comprehensive overview of this growing field of international migration law. It brings together and critically analyses the disparate norms of treaty law, customary law, and soft law on a broad variety of issues, such as irregular migration, human trafficking, refugee protection, labour migration, non-discrimination, regional free movement schemes, and global migration governance. It also offers a particular focus on specific groups of migrants, namely migrant workers, refugees, smuggled migrants, and victims of human trafficking. It maps the current status of the law governing their movement, providing a thorough critical analysis of the various strands of international law which apply to them, suggesting how the law may continue to develop in the future.