SummaryAn historical review of the closely related generaCiboriaandSclerotiniais given.The non-validity of the generaRutstroemiaandStromatiniahas been discussed.Type species for these four genera have been designated following the principle of types as outlined in the American code of botanical nomenclature.A basis for the classification of the genusSclerotinia, as recognized up to the present, is indicated.A new genus,Monilinia, is created to include the monilioid forms which show a genetic relationship to the genusSclerotinia. Monilinia fructicola(Wint.) Honey (=Sclerotinia fructicola(Wint.) Rehm) is designated as the type species of the genusMonilinia.The writer wishes to express his appreciation to the various individuals to whom he has been indebted during the preparation of this article: to Professor Whetzel for the suggestion of the problem of which this is an outgrowth; to Dr. L. M. Massey for the photographic privileges of the Department of Plant Pathology of Cornell University; to Dr. C. L. Shear for the privilege of examining the cotype material; to Dr. E. M. Gilbert, Dr. G. W. Keitt, Dr. A. J. Riker and Dr. Regina Stockhausen Riker for the critical reading of the manuscript; and to Dr. Fred J. Seaver for kindly suggestions concerning the manuscript.