Great Smoky Mountains National Park is renowned as one of the most biologically diverse tracts of land in North America and is the most visited national park in the United States. The park comprises ∼830 square miles, epitomizes eastern temperate hardwood forests of North America, and serves as a refuge for nearly 20,000 documented species from microbes to plants and mammals. Lichens comprise one particularly diverse group of organisms in the park. In this study, we review data from our 11 years of lichenological research in Great Smoky Mountains National Park. Based on approximately 6,000 new field collections generated, the park checklist now includes 920 species, a 129% increase over estimates made two decades ago. Nearly a quarter of the lichens reported in the park are known from only a single occurence whereas only 7% of the lichens are known from 20 or more occurences. An assessment of commonness/rarity for all 920 species indicates that nearly half of the park's lichens should be considered to be infrequent, rare, or exceptionally rare. We assessed the distributions of all 920 species and found that 54 are endemic to the southeastern United States, 30 are endemic to the southern Appalachians, and eight occur nowhere else than within the confines of the national park. We discuss biogeographical affinities of the park's lichen biota as a whole, delimiting six regional “floristic” connections. Our 11 years of research have resulted in the discovery of several species presumed to be extinct or near-extinct. We make one new combination (Fuscopannaria frullaniae) and describe five species as new to science, each commemorating National Park Service staff instrumental to the completion of the study: Heterodermia langdoniana, Lecanora darlingiae, Lecanora sachsiana, Leprocaulon nicholsiae, and Pertusaria superiana.