Ukrainian Underground Post

The Ukrainian Underground Post or Underground Post of Ukraine (Ukrainian: Підпільна пошта України, romanized: Pidpilna poshta Ukrainy), commonly abbreviated as PPU, was an internationally unrecognized Ukrainian diaspora postal agency based in Munich, West Germany, and in Chicago, United States that released cinderella stamps worldwide from its opening in 1949 until its closure in 1983. The Ukrainian war veteran and prisoner of war Stepan Liubomyr Rychtyckyj developed an interest in philately and, with Julian Maksymchuk, helped to found the organisation in West Germany. It operated under a branch of the Organisation of Ukrainian Nationalists, an authoritarian nationalist organisation that sought a Ukrainian state independent from the Soviet Union after its annexation of the Ukrainian People's Republic in 1921.

The PPU stamps celebrated Ukrainian nationalism by promoting Ukrainian organisations/institutions, events, and famous individuals in its stamp designs, which were designed by pools of distinguished artists. In total, it had issued more than 3,700 postal stamp issues, which were diverse in paper types and colors. The stamps were utilised for propaganda purposes and helped to fund the OUN's resistance purposes against the Soviet Union and were not sold by the government of the Ukrainian People's Republic in exile. The Ukrainian Underground Post issued its last issues and then closed in 1983, the same year that the agency's chief Rychtyckyj died.