During the war years, 18.2 million men served in the German armed forces. Each of them had family members with whom they kept in touch by letter through the field post. For this reason, field post letters are still among the most common and widely distributed sources today.

Mostly, these letters remained in the possession of families and were only rarely - in proportion to their distribution - collected by archives, such as the Museum für Kommunikation (Museum of Communication) in Berlin. Among the best-known collections are the Sterz Collection and the Schüling Collection, both of which are kept in the Landesbibliothek (state library) in Stuttgart. Only a vanishingly small proportion of these documents have been edited and made accessible to scholars.

As a source for historiography, the field post letters were discovered in West Germany in the 1980s and 1990s as a source for reconstructing everyday life.