A small herd of woodland caribou (Rangifer tarandus caribou) in the southern Selkirk Mountains of British Columbia and Idaho are the only caribou in the United States outside of Alaska. We initiated studies to determine caribou habitat use in 6 time periods (seasons) and to develop standards for the protection of habitat essential for recovery of this endangered herd. We described habitats for each season by measurements of basal area, tree density, canopy cover, understory cover, lichen abundance, slope, aspect, elevation, and timber stand type. These parameters and the habitat components they described were then related to environmental variables, caribou behavior patterns, and physiological requirements of caribou in each season. Snow cover and firmness, isolation of females during calving, and summer and winter forage requirements are discussed as they relate to use of habitat components. Recommendations for habitat management identify those components essential for recovery of caribou in the Selkirk Mountains.