Citizen patrols are organized groups of volunteers who actively engage in activities aimed at deterring and reducing crime in their communities. These patrol groups can be found throughout the world, are diverse in their member demographics and organizational structures, and often work directly with specific police agencies. As with other forms of positive citizen engagement with the police, citizen patrols can complement community policing and problem solving by providing a coordinated approach to crime fighting and enhancing police efforts. This entry describes various types of citizen patrols found within the United States, the purpose and general functions of these groups, research findings concerning their impact on crime levels, and the major controversies surrounding citizen patrol organizations.