<P>International organizations are the capitals of global governance with many functions from policy making and implementation; to peacekeeping and post-conflict reconstruction and development. They also organize the international flow of knowledge and have become a key building block of the epistemic foundations of international relations. </P><P></P><P>This book challenges traditional models that treats IOs either as passive, technical infrastructures for states, or ‘states + bureaucracy’, to argue for an understanding of IOs as sites that host practice. Drawing on theorizing from the ‘practice turn’ in IR theory, organizational studies and science and technology studies, it develops a different understanding of IOs which pays close attention to the diverse actions that perpetuate an IO, including the actions of statesmen, bureaucrats, activists, and researchers. The author uses the United Nations peacebuilding work as a case to demonstrate the value of practice based theorizing and methodology. Peacebuilding is a paradigmatic case as it expresses many of the challenges of contemporary global governance, including high epistemic uncertainty, weak institutional structures, high liquidity and a multiplicity of actors. </P><P></P><P>Providing a new analytical perspective on IOs this book will be of strong interest to students and scholars of international relations, international relations theory, international organizations and peacebuilding.</P>