International Relations (IR) theory has been the site of intense debate in recent years. A decade ago it was still possible to divide the field between three main perspectives - realism, liberalism and Marxism. Not only have these approaches evolved in new directions, they have been joined by a number of new 'isms' vying for attention, including feminism and constructivism. International Relations Theory for the Twenty-First Century is the first comprehensive book to provide a critical overview of all the most important theories within the study of international relations. Written by a team of international experts in the field, the book covers both traditional approaches as well as new developments within IR theory.