Groszy Overprints Site dedicated to the groszy overprints of 1950. It utilizes the exhibit material of Polonus member George Zelwinder to identify and illustrate the different overprints used during the currency devaluation. See George's exhibit in the "Exhibits" section of the Polonus website.
Stamp Domain An comprehensive philatelic site providing data on stamps of the world including an excellent section pertaining to the Stamps of Poland
Stamp Encyclopedia of Poland An extremely comprehensive listing of all the areas of Polish philately including regular issues, local issues, P.O.W issues and Labels. Virtually all issues items are described this comprehensive vast wealth of information. Text is in English