Abstract: This is an introduction to a series of papers devoted to the mapping of the polypore species occurring in Finland. The survey is based on the Finnish national uniform grid system (Grid 27°E), whose unit is 10 X 10 km. For each distribution map all the material available in public Finnish herbaria has been consulted. It is planned to publish the maps at irregular intervals. The principles of the mapping are presented and the biogeography of Finland briefly discussed. The names are given of the most important indigenous and cultivated tree species infected by polypores in Finland.