Book excerpt: The volume is the first comprehensive overview of multiple theoretical perspectives on UN peace operations, with two main uses. First, it provides practical examples of how International Relations theories - realism, liberal institutionalism, rational choice institutionalism, sociological institutionalism, constructivism, practice theories, critical security studies, feminist institutionalism, and complexity theory - can be applied to a specific policy issue. Second, it demonstrates how major debates on UN peace operations - regarding protection of civilians, local ownership, or gender mainstreaming - benefit from a theoretical exploration. The volume is aimed at three audiences: scholars who want to keep up to date with the latest research on UN peace operations; undergraduate and postgraduate students who either seek to understand International Relations theories in general or are interested in UN peace operations..