What This projects explores a key feature of modern international organisations: international bureaucracies. In recent years, international bureaucratic bodies, and the EU bureaucracy in particular, have come under attack for being intransparent and undemocratic. Yet, in a globalized world, they are indispensable. This book offers the first historical exploration of the emergence and development of 20th century international bureaucracy. Investigating the professional norms and practices of these institutions, the power they held and how they have evolved since the foundational inter-war years, it moves beyond the normative assumptions of these organisations as good or bad and generate fundamentally new insights into the genealogy and constitutive elements of international bureaucracies today. Why Over the last 100 years, more than 5000 international organisations have been set up to deal with the many problems and challenges emerging from an increasingly globalized world. This mushrooming of international organisations has not only shifted power from the national to the international level but also from national parliaments towards legal and executive forms of power. This shift has created challenges of political legitimacy for IOs that they are still struggling to address. The book is important because it sheds light on this problem and help us understand the social characteristics and political power associated with international bureaucratic bodies. How The book will be based on primary sources generated through multi-archival research into IO and government archives as well as private papers of central decision makers. The account draws on 20 different archival collections in nine different countries. SSR The book's historical exploration of the emergence and development of international bureaucracy offers critically important historical context to our understanding of this at once indispensable, intransparent and highly contested form of power.