Three main arguments are made in the success in reconstructing internal security: (1) establishing security during the “golden hour” should be the most immediate concern of policymakers after the conclusion of major combat operations; (2) in addition to reconstructing and reforming the police and security forces, a viable justice system must be established; and (3) identified minimum resource levels in the areas of international troops and police, domestic police, assistance, and duration, should be established to maintain security. In addition, six policy recommendations for the United States policy on post-conflict internal security include: (1) give as much attention to planning post-conflict internal security as to planning combat operations; (2) negotiate a peace treaty or formal surrender; (3) fill the security gap quickly with United States (and allied) military and constabulary forces; (4) develop comprehensive doctrine for post-conflict internal security reconstruction; (5) build mechanisms to ensure faster mobilization of personnel, funds, and equipment; and (6) focus on outcome measures to shape programs. Providing security and reconstructing internal security institutions is a key component of nation-building operations. They are also vital to lay the foundation for a strong and legitimate state. This study examined how successful the United States and allied efforts have been in reconstructing internal security institutions and what are the most important lessons for current and future operations. To answer these questions, the study compared the results with data from six other cases in which the United States has helped reconstruct security institutions during nation-building missions: Panama, El Salvador, Somalia, Haiti, Bosnia, and East Timor. Figures, tables and references