The Lichen Flora of the United States, first published in 1935, is made available again in answer to numerous requests.The manual presents a general discussion of the morphology and reproduction of the group. There are descriptions of 1,578 species, varieties, and forms, belonging to 178 genera and 46 families. Keys to the families, genera, and species, 47 plates illustrating 63 species, and an index complete the volume.