A conscientious objector (often shortened to conchie) is an "individual who has claimed the right to refuse to perform military service" on the grounds of freedom of thought, conscience, or religion. The term has also been extended to objecting to working for the military–industrial complex due to a crisis of conscience. In some countries, conscientious objectors are assigned to an alternative civilian service as a substitute for conscription or military service.

A number of organizations around the world celebrate the principle on May 15 as International Conscientious Objection Day.

On March 8, 1995, the United Nations Commission on Human Rights resolution 1995/83 stated that "persons performing military service should not be excluded from the right to have conscientious objections to military service". This was re-affirmed on April 22, 1998, when resolution 1998/77 recognized that "persons [already] performing military service may develop conscientious objections".