Auxiliary may refer to:

  • A backup site or system
  • Auxiliary input jack, generally for audio
  • Auxiliary verb
  • International auxiliary language
  • Auxiliary police
  • Auxiliaries, troops supporting the main force of an army
    • Auxiliaries (Roman military)
  • Auxiliary route, also known as "special route", in road transportation
    • An auxiliary route of the Interstate Highway System in the United States
  • Auxiliary bishop, in the Roman Catholic Church
  • Auxiliary organization in the Latter Day Saint movement
  • Aux-send of a mixing console
  • A marching band colorguard