This “white paper” simply defines the police forces of Mexico, describes police organizations and identifies some of their major challenges. Mexican police institutions are complex, multifarious and changing; as a result, function and jurisdiction emerge as two key ways to understand the police. The major challenges to making the police more efficient, effective and accountable are the lack of resources, poor training, corruption and increasingly severe crime problems. This paper is intended as a resource and is a work in progress; comments, corrections and updates are welcome.