This book contends that practices are perhaps the most fundamental building-block of social reality. What then would social scientists’ research look like if they took this insight seriously? The book argues that to be effective, social-scientific inquiry requires the detailed empirical study of human practices. At the same time, it makes a case for the central place in social theory and the philosophy of the social sciences of a well-developed practice theory. To be sure, conventional research in the social sciences has always investigated regularities of human behaviour; yet its core assumptions, the author argues, leave it ill-equipped to cope with essential features of the phenomena it investigates. This book is thus devoted to examining what these generic features of human practices are. In the process, it also explores how practices are constituted; how they can be identified, characterised and explained; how they function in concrete contexts; and how they might change across time and space. Noting that existing versions of practice theory often face important analytical problems, the book attempts to construct a new, systematic account from the ground up. Along the way, it illustrates its arguments with many concrete examples from the history of war, politics and intellectual currents in Europe, as well as from various domains in the social sciences and everyday life. Kevin McMillan is an Associate Professor in the School of Political Studies at the University of Ottawa and co-coordinator of the International Theory Network (ITN). His research interests include IR theory, modern and early-modern international history, the evolution of the European states system since 1648, history of international thought, governance, practice theory and the philosophy of the social sciences.