A lateen (from French latine, meaning "Latin") or latin-rig is a triangular sail set on a long yard mounted at an angle on the mast, and running in a fore-and-aft direction. The settee can be considered to be an associated type of the same overall category of sail.

The lateen originated in the Mediterranean as early as the 2nd century CE, during Roman times, and became common there by the 5th century. The wider introduction of lateen rig at this time coincided with a reduction in the use of the Mediterranean square rig of the classical era. Since the performance of these two rigs is broadly similar, it is suggested that the change from one to the other was on cost grounds, since lateen used fewer components and had less cordage to be replaced when it wore out.

Arab seafarers adopted the lateen rig at a later date – there is some limited archaeological evidence of lateen rig in the Indian Ocean in the 13th century CE and iconographic evidence from the 16th century. It has been suggested that this Arab use of lateen transferred to Austronesian maritime technology in the Far East, giving rise to the various fore and aft rigs used in that region, such as the crab claw sail.

The lateen sail played a prominent part in the shifts in maritime technology that occurred as Mediterranean and Northern ship construction traditions merged in the 16th century, with the lateen mizzen being, for a time, universally used in the full-rigged ships of the time – though later supplanted gaff rig in this role.