The first definitive series was issued in 1922 and we are now on the 9th Definitive Series.
The same designs were in use until 1968 when the notable Gerl early art definitives were issued. They were replaced in 1982 by Michael Craig's archictecture series. In 1990 An Post introduced the Irish Heritage and Treasure series followed by Irish Birds in 1997.
The latest definitive issue theme is Irish Flowers which have been issued since 2005