In the United States armed forces, Officer Candidate School (OCS) or the equivalent is a training program for non-commissioned officers, soldiers, sailors, marines, airmen and recent college graduates to earn commissions as officers. The courses generally last from ten to twelve weeks and include classroom instruction in military subjects, physical training, and leadership preparation.

People may earn a commission in the United States armed forces through OCS or OTS, by staff appointment, through ROTC, or through one of the four military academies.

The Officer Candidates School of the United States Marine Corps, the initial training of Marine officers, is at Marine Corps Base Quantico.

The Officer Candidates School of the United States Navy is in Pensacola, Florida.

The Officer Candidates School of the United States Army is at Fort Benning, Georgia.

The Officer Training School of the United States Air Force is at Maxwell AFB, Alabama.