For many years there has been a great need for a critical and comprehensive study of the genus Clitocybe. This fact has become evident to all who have worked in the genus. Aside from a few common and distinctive species, it is difficult and often impossible to identify a Clitocybe correctly from the literature. ... Over a thousand species have been described in the genus Clitocybe, but the majority cannot be identified from their descriptions. The purpose of this paper is to present an account of the Clitocybe flora of Michigan. In order to avoid the faults of previous works emphasis has been placed on the following points. 1. Type material has been studied where ever possible. ... 2. The published descriptions and illustrations were thoroughly checked, as well as unpublished information. 3. When type material was not available, as in the case of the Friesian species, emphasis was placed on the original description rather than on subsequent interpretations. 4. Variation has been studied by means of the technique of mass collecting. Emphasis has been placed on extensive field work during all seasons in order to determine any variations in the fruiting of Clitocybes caused by fluctuations in moisture and temperature. 5. Several hundred extralimital collections have been examined by the writer in order to obtain the broadest base possible for interpreting the Michigan Clitocybes.