The Ascomycete genus Monilinia Honey with its anamorph Monilia includes many parasites of woody perennials, including economically important fruit-trees. This study treats the morphology in vivo and in vitro and detailed life histories; it evaluates, describes and selects criteria for the generic and infrageneric definition of taxa; it discusses host-pathogen interactions, symptoms, nature of losses, extent of host-specificity of the various species, including cross-inoculation work in the greenhouse, and reviews control measures for the eight economically important species. Two dichotomic keys facilitate the identification of the taxa.