Drawing on insights from differentiation theory, this book examines the participation of middle powers in multilateralism.Taking Australia, Indonesia and South Korea as examples, the book examines these countries’ roles in regional organizations, and particularly their creation of the Asia-Pacific Economic Cooperation (APEC) and East Asia Summit. Through its analysis, the book argues that middle powers pursue a weakening of ‘stratificatory differentiation’, targeted in particular at major powers, and a strengthening of ‘functional differentiation’ in which middle powers can assume key roles.The book sets out a valuable new framework to explain and understand the behaviour of middle powers in multilateralism.