The postage stamps of Ireland are issued by the postal operator of the independent Irish state. Ireland was part of the United Kingdom of Great Britain and Ireland when the world's first postage stamps were issued in 1840. These stamps, and all subsequent British issues, were used throughout Ireland until the new Irish Government assumed power in 1922. Beginning on 17 February 1922, existing British stamps were overprinted with Irish text to provide some definitives until separate Irish issues became available within the new Irish Free State. Following the overprints, a regular series of definitive stamps was produced by the new Department of Posts and Telegraphs, using domestic designs. These definitives were issued on 6 December 1922, the day that the Irish Free State officially came into existence; the first was a 2d stamp, depicting a map of Ireland. Since then new images, and additional values as needed, have produced nine definitive series of different designs.

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.