The present-day northern Rocky Mountain vegetation is the product of a long history of geologic and climatic events that have interacted with the species populations composing the regional flora. General concepts relating to the organization, classification, and dynamic nature of vegetation are reviewed. Distributional and structural features of the vegetation cover between the Colorado Rockies and the Southern Canadian Rockies are discussed. Alpine, upper timberline, subalpine, montane, lower timberline, and grassland/steppe zones are treated. Climatic, physiographic, edaphic, and geologic factors operate interactively as complex local and regional gradients in patterning Rocky Mountain vegetation. It is likely that members of the modern Rocky Mountain flora are not in equilibrium with present-day environments but are shifting and adjusting to geographic dislocations associated with post-Pleistocene climatic alterations. Fire supperssion, agriculture, domestic grazing, construction activities, timber harvesting, strip mining, species introductions, and air, soil, and water quality are having major impacts on Rocky Mountain vegetation. Present plant communities feature altered structures and compositions that may represent new ecosystem equilibria which could be irreversible under present-day climates.