Sergeant (abbreviated to Sgt. and capitalized when used as a named person's title) is a rank in use by the armed forces of many countries. It is also a police rank in some police services. The alternative spelling, serjeant, is used in The Rifles and other units that draw their heritage from the British light infantry. Its origin is the Latin serviens, 'one who serves', through the French term sergeant.

The term sergeant refers to a non-commissioned officer placed above the rank of a corporal, and a police officer immediately below a lieutenant in the US, and below an inspector in the UK. In most armies, the rank of sergeant corresponds to command of a squad (or section). In Commonwealth armies, it is a more senior rank, corresponding roughly to a platoon second-in-command. In the United States Army, sergeant is a more junior rank corresponding to a squad- (12 person) or platoon- (36 person) leader.

More senior non-commissioned ranks are often variations on sergeant, for example staff sergeant, gunnery sergeant, master sergeant, first sergeant, and sergeant major.

In many nations and services, the rank insignia for a sergeant often features three chevrons.