An overprint is an additional layer of text or graphics added to the face of a postage or revenue stamp, postal stationery, banknote or ticket after it has been printed. Post offices most often use overprints for internal administrative purposes such as accounting but they are also employed in public mail. Well-recognized varieties include commemorative overprints which are produced for their public appeal and command significant interest in the field of philately.

Postal service in the United States began with the delivery of stampless letters whose cost was borne by the receiving person, later encompassed pre-paid letters carried by private mail carriers and provisional post offices, and culminated in a system of universal prepayment that required all letters to bear nationally issued adhesive postage stamps.