Katahdin, the highest peak in Maine at 1606 m, has about 13 km² (1300 ha) of alpine and subalpine tundra and krummholz on a summit plateau and in upper cirque basins. Lichens and bryophytes have been collected above tree line since the mid-19^th century, but the cryptogam biota of the mountain has remained incompletely documented. For 16 days during 2001–2004 we inventoried lichens and bryophytes of the subalpine and alpine zones of Katahdin (above 884 m), visiting open alpine tundra, alpine cliffs in glacial cirques, seeps, fellfields, krummholz and subalpine forests. We relocated most species represented by historic collections and added many more to the documented biota, including significant range extensions and species new to North America or northeastern United States. The floristic results are presented in two associated papers. Here we (1) summarize previous studies of the botany, ecology and geology of Katahdin; (2) compare quadrats from a Diapensia heath in exposed alpine tundra on the Table Land with a snow bed community just below the Table Land, where a marked difference in the bryophyte and lichen assemblages may reflect cryptogam-vascular plant interactions and/or site-specific differences; and (3) summarize unpublished weather data collected at the Chimney Pond Ranger Station (ca. 890 m). Katahdin and Mt. Washington, New Hampshire, have similar recent temperature and precipitation records on the basis of the available data. Katahdin shares some vegetation components and climate features with mountain ranges in the Pacific Northwest, New Zealand and the Scottish Highlands that have been studied for lichens and/or bryophytes.