SummaryThe taxonomic position of certain species of Sclerotinia and Monilia which cause disease of fruits has for many years been in a chaotic state. In order to correct this confusion the following dicta are proposed. 1. Names of species to be valid must be accompanied by adequate descriptions, properly published.2. Assumptions that species of Monilia have species of Sclerotinia as ascogenous stages are permissible but scientific names based on unknown ascogenous forms are not valid.3. Whenever possible the connection between a species of Sclerotinia and a species of Monilia must be demonstrated, if it is to be accepted.With these dicta as a guide a critical review of the literature and their own studies lead the authors to conclude: 1. Two species occur on drupaceous and pomaceous fruits in America, one being the common brown-rot fungus and the other a recently discovered form occurring along the Pacific Coast.2. The common form the writers now believe to be a species distinct from any known European form.3. The correct name of the common form is Sclerotinia fructicola (Wint.) Rehm.4. The Pacific Coast form is similar to and possibly identical with Monilia cinerea of Europe. No perfect stage of this fungus has been found in this country.5. Sclerotinia fructigena is a valid name for a fungus occurring in Europe but not known to occur in the United States.