After decades of police reforms around the world, there is no general formula for what works and what does not work in such processes. Based on a review of diverse research, this policy brief describes the challenges of police reforms, particularly in countries emerging from armed conflict, where the police must transition from being militarized to democratic policing. Most reform efforts around the world have had mixed results, with few truly successful experiences, both due to reform and external factors. The policy brief stresses the importance of better cooperation between international actors and local authorities, as well as strong state support, a clear separation between military and police tasks, and thorough background checks of police personnel. It is also important to improve relations between the police and communities in order to achieve sustainable results.