A commissary is a government official charged with oversight or an ecclesiastical official who exercises in special circumstances the jurisdiction of a bishop.

In many countries, the term is used as an administrative or police title. It often corresponds to the command of a police station, which is then known as a "commissariat". In some armed forces, commissaries are officials charged with overseeing the purchase and delivery of supplies, and they have powers of administrative and financial oversight. Then, the "commissariat" is the organization associated with the corps of commissaries. By extension, the term "commissary" came to be used for the building where supplies were disbursed.

In some countries, both roles are used; for example, France uses "police commissaries" (commissaires de police) in the French National Police and "armed forces commissaries" (commissaires des armées) in the French armed forces.

The equivalent terms are commissaire in French, commissario in Italian, Kommissar in Standard German, Kommissär in Swiss German and Luxembourgish, comisario in Spanish, commissaris in Dutch and Flemish, komisario in Finnish, komisarz in Polish and comissário in Portuguese. Many of these words may also mean commissioner, depending on the context.