It is an era of expansion for the International Organization for Migration (IOM), an increasingly influential actor in the global governance of migration. Bringing together leading experts in international law and international relations, this collection examines the dynamics and implications of IOM's expansion in a new way. Analyzing IOM as an international organization (IO), the book illuminates the practices, obligations and accountability of this powerful but controversial actor, advancing understanding of IOM itself and broader struggles for IO accountability. The contributions explore key, yet often under-researched, IOM activities including its role in humanitarian emergencies, internal displacement, data collection, ethical labour recruitment, and migrant detention. Offering recommendations for reforms rooted in empirical evidence and careful normative analysis, this is a vital resource for all those interested in the obligations and accountability of international organizations, and in the field of migration. This title is also available as Open Access on Cambridge Core.