Functional differentiation has long been at the heart of sociological thought, and as such has become a defining feature in the evolution of modern society; one which distinguishes it from pre-modern societies which have instead typically differentiated by means of segmentation, or stratified social systems such as class. Drawing on the latest developments on differentiation theory in international relations and sociology, this book brings together contributions from leading IR scholars and sociological theorists to offer a unique interdisciplinary synthesis in which contemporary world politics is discussed as a differentiated social realm. Bringing Sociology to International Relations is an illuminating and innovative new resource for scholars and students which strives to respond to a significant question across all its chapters: what happens when this well-established sociological theoretical framework is transposed from the domestic level, for which it was originally designed, to the larger and more complex subject of international relations?