Harry von Hofmann (2000). Latvia, Handbook of Philately and Postal History. The Stamps, Lat Period 1923-1940. Harry von Hofmann Verlag. ISBN3-7636-5073-3.
Philatelic Society of Latvia (2007). Specialized Catalogue of Postage Stamps and Postal Stationery of Latvia. Philatelic Society of Latvia. ISBN9984-9126-9-8.