Peace operations involve the expeditionary use of uniformed personnel (police and/or military) whose mission is to help secure “international peace and security.” In many ways, peace operations are the most visible activity of the United Nations with a mandate to deter armed conflict through preventive deployment or help to kick-start a peace process through peacemaking initiatives, among other purposes. Peace operations can be grouped into several categories, including preventive diplomacy, peacemaking, peacekeeping, post-conflict peacebuilding, and peace enforcement. There are three clusters of approaches that have tried to think conceptually about the relationship between peace operations and broader processes of global politics: global culture, critical theory, and cosmopolitanism. Questions of success and failure in peace operations have been tackled in the literature, which includes the UN’s own reports as well as books and articles appearing within a range of academic disciplines. Scholars have also analyzed the many challenges facing peace operations ranging from civilian protection and gender issues to public security and policing, privatization, intelligence provision, and state-building. Overcoming these challenges will require, at a minimum, new ways of thinking about the problems concerned, new ways of organizing the relevant institutions, and getting the would-be state-builders to allocate substantial resources. There are also some important questions that deserve greater attention; for example, what types of non-UN peace operations are most effective, under what conditions, and how they compare with UN operations, or how a world order can be constructed in which the peacekeepers have put themselves out of business.