This introductory textbook on international relations theory brings together a selection of leading experts to offer an unparalleled insight into the main paradigms and latest developments in the discipline. Presenting a full range of theories, from realism and liberalism to institutionalism and green theory, the sixth edition of this book has been extensively revised to offer a more global introduction to international relations. It showcases insights from across the world, and employs a historical and sociological perspective throughout to demonstrate how any understanding of IR is time and place contingent. New to this edition are two new chapters on postcolonialism and institutionalism, as well as boxed cases which apply theory to contemporary empirical examples including gendered policy in the UN, the phenomenon of 'fake news', issues on migration, and the crisis of the Amazon's forest fires. Assuming no prior knowledge of international relations theory, this text remains the definitive companion for all students of international relations and anyone with an interest in the latest scholarship of this fascinating field.