AUX or aux may refer to:
Auxiliary police, also called Special Police, are usually the part-time reserves of a regular police force.
An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion.
Auxonne is a French commune in the Côte-d'Or department in the Burgundy region of eastern France. The inhabitants of the commune are known as Auxonnais or Auxonnaises.
An auxiliary verb (abbreviated aux) is a verb that adds functional or grammatical meaning to the clause in which it appears, such as to express tense, aspect, modality, voice, emphasis, etc.