The purpose of this study is to provide investigators of the Great Lakes Region with an accurate classification of the species of Clavaria Fries. Attention has been given to the more recently segregated smaller genera which some authors have considered distinct. The segregates have been studied in terms of an evaluation of the characters used to distinguish them. Sixty-four species are described from Michigan. Among these, C. caulifloriformis, C. fuscoferruginea, C. rubicundula, C. phycophila, C. botrytis var latispora, C. luteo-tenerrima var. borealis and C. pulchra var. globulina are described as new. In addition to the foregoing, thirteen species and five varieties are reported from Michigan for the first time while five species and one variety constitute first reports from the United States. Keys to the identification of all sixty-four species are provided. The spores of each have been illustrated. Photographs of thirty-four species have also been included. The characters most generally used in the classification of species have been evaluated from a study of their occurrence in both fresh and dried material. Those which have been found valuable for arranging species into large groups are: color of the reaction in ferric sulphate, shape of the fructification, spore ornamentation, shape, and color of the spore deposit. Characters which have proven worthy of emphasis in separating species include the following: taste and odor, color and color changes; spore size, type of ornamentation and the presence of an amyloid reaction; the presence or absence of cystidia and their type, if present. Additional information has been presented concerning many species. Among these, C. pyxidata var. pyxidata is shown to have amyloid spores. A study of the type of C. cacao shows that the species possesses diagonally striate spores. The occurrence of clamp connections appears to have some value at the species level in the section Ramaria but the character is so variable in the other groups that it is not considered as reliable in distinguishing those species. Comparisons of basidial size with that of the fructification show the largest fruiting bodies to possess the largest basidia. Variation of many of the characters most generally used in separating smaller genera from Clavaria Fries has been shown to be so great that several of the smaller segregates, as embodied in the monograph of Corner (1950), are not recognizable taxa. Clavarioid fungi were found to be most numerous in forest communities where hemlock, white pine and yellow birch are the dominant trees. Most species are terrestrial and appear restricted to heavily shaded areas where there is a rich layer of humus.