A comprehensive treatment of the population biology of fungi. Intended for mycologists as well as biologists without mycological background, it includes detailed coverage of all major taxonomic groups for which information is available and key topics in depth, including species concepts, somatic incompatibility, gene flow, role of sexual vs. asexual reproduction, mycoviruses, demography and fitness. Kinds and patterns of intraspecific variation are considered, including quantitative and especially molecular characteristics. Throughout, an attempt is made to relate aspects of fungal population biology to biology as a whole.