A total of 293 different lichens (and lichenicolous fungi) were found above an elevation of 884 m on Katahdin during fieldwork from 2000 to 2004 and from study of previously collected herbarium specimens. Thirteen of these are new to North America, 39 additional lichens are new to northeastern United States and 26 additional ones are new to Maine; three additional taxa are almost certainly new to science but are not formally described in this study. We identified eight distinct lichen habitats on Katahdin: (1) A1, exposed alpine tundra and fellfields; (2) A2, high elevation alpine sites protected from northwest winds; (3) A3, east-facing alpine late-snow areas; (4) A4, alpine krummholz; (5) A5, cirque headwalls facing east and north; (6) A6, cirque headwall facing southeast; (7) B1, exposed low-altitude tundra, talus and krummholz; and (8) B2, subalpine forests. Each habitat except A4 had numerous lichens (10–56 taxa) found in none of the others, and each differed statistically from two to six other habitats by a quantitative measure of the Arctic-boreal-temperate (ABT) distribution of its lichens. Habitat A3 had, on average, the most Arctic lichens, followed by A1, A2, A5, B1, A6 and A4, with B2 having the fewest Arctic lichens and the most with a temperate distribution. Lichen ABT values for the eight habitats are well predicted (R²  =  96.9%) by a multiple regression equation incorporating three independent variables: average elevation above sea level of the lichens collected in a habitat class; an estimate of solar gain for each of the eight habitats; and the presence or absence of trees (including krummholz). We compared our results with those for Mt. Albert, Gaspé, Quebec, the only other comprehensive study of alpine lichens in northeastern North America, for such parameters as species presence/absence, substrata and ABT value. We suggest that future studies looking into effects of global warming or increases or decreases in air pollution will be facilitated by the study of certain habitats rather than the entire alpine and subalpine Katahdin region.