“Nation-building” is an increasingly frequent activity of Western governments and the United Nations, with Kosovo an important recent example. This study examines the reconstruction by the United Nations of Kosovo’s internal security infrastructure from 1999 to 2004. It analyzes United Nations and other activities to build democratic police and justice systems. Through a model of security reconstruction, it examines in detail the primary security challenges facing Kosovo, the specific efforts the United Nations made to address these challenges, the ultimate effectiveness of the reconstruction in establishing stability and rule of law, and the linkages between reconstruction efforts and democracy. It concludes with several lessons for improving the effectiveness of such efforts in the future.