The monograph summarizes data on 1256 species and infraspecific taxa of lichens and taxonomically adjacent fungi, reported for the Republic of Karelia, including 1097 taxa of true lichens (lichenized fungi), 137 taxa of lichenicolous fungi, 22 species of non-lichenized fungi taxonomically close to lichens. 16 species are reported for Karelia for the first time. A number of species and infraspecific taxa in each biogeographic province (floristic district) of Karelia is given. The publication is meant first of all for specialists in lichenology, mycology, as well as for biologists, professors and students of natural sciences, and conservationists.