The 15th United States Infantry Regiment is a parent regiment in the United States Army. It has a lineage tracing back to the American Civil War, having participated in many battles.

The official Army history and lineage does not credit the current 15th Infantry with the honors or lineage of these earlier regiments.

The first 15th Infantry in the U.S. Army was organized on 16 July 1798 for the "Quasi-War" with France. The regiment saw no war service and was inactivated in 1800. A second 15th Infantry was activated in 1812 in New Jersey for service in Canada during the War of 1812. The 15th fought in the capture of Toronto and Fort George in April and May 1813, and covered the retreat of militia troops from Fort George in December 1813. A portion of the 15th were the last American troops to abandon Cornwall during the St. Lawrence Campaign of 1813. In this retreat, no member of the 15th was captured, despite taking heavy casualties. The 15th fought in the Champlain Valley campaign in autumn 1814 at Plattsburgh, and participated in General Dearborn's offensive in Ontario in October, and took part in many smaller battles that same year. The regiment was eliminated in the Army reorganization of 1815.