Officer candidate or officer aspirant (OA) is a rank in some militaries of the world that is an appointed position while a person is in training to become an officer. More often than not, an officer candidate was a civilian who applied to join the military directly as an officer. Officer candidates are, therefore, not considered of the same status as enlisted personnel.

In several NATO countries, the term officer designate (OF-D) is used. In the NATO rank scale, it comes below the grade of OF-1 and above the grade of Student Officer. Ranks designated as OF-D include dokimos efedros axiomatikos in the Hellenic Army, and chuẩn úy ("officer designate") in the Vietnam People's Army. In the German Armed Forces, officer designates are enlisted personnel and have a corresponding rank code.