Rocky Mountains, byname the Rockies, mountain range forming the cordilleran backbone of the great upland system that dominates the western North American continent. Generally, the ranges included in the Rockies stretch from northern Alberta and British Columbia southward to New Mexico, a distance of some 3,000 miles (4,800 km). In places the system is 300 or more miles wide. Limits are mostly arbitrary, especially in the far northwest, where mountain systems such as the Brooks Range of Alaska are sometimes included. The Rockies are bordered on the east by the Great Plains and on the west by the Interior Plateau and Coast Mountains of Canada and the Columbia Plateau and Basin and Range Province of the United States.

The Rocky Mountains include at least 100 separate ranges, which are generally divided into four broad groupings: the Canadian Rockies and Northern Rockies of Montana and northeastern Idaho; the Middle Rockies of Wyoming, Utah, and southeastern Idaho; the Southern Rockies, mainly in Colorado and New Mexico; and the Colorado Plateau in the Four Corners region of Utah, Colorado, New Mexico, and Arizona. These four subdivisions differ from each other in terms of geology (origin, ages, and types of rocks) and physiography (landforms, drainage, and soils), yet they share the physical attributes of high elevations (many peaks exceeding 13,000 feet [4,000 metres]), great local relief (typically 5,000 to 7,000 feet in vertical difference between the base and summit of ranges), shallow soils, considerable mineral wealth, spectacular scenery from past glaciation and volcanic activity, and common trends in climate, biogeography, culture, economy, and exploration.

The Columbia Icefield is situated on the continental divide in the Canadian Rockies at elevations of 10,000 to 13,000 feet (3,000 to 4,000 metres) above sea level. It includes the large Athabasca Glacier, which is nearly five miles long and about a mile wide. Glaciers in this ice field, while continuing to move, are thinning and retreating. The Canadian Rockies are about equally divided between drainage to the east (Atlantic and Arctic oceans) and west (Pacific Ocean).

The Middle Rockies include the Bighorn and Wind River ranges in Wyoming, the Wasatch Range of southeastern Idaho and northern Utah, and the Uinta Mountains of northeastern Utah; the Absaroka Range, extending from northwestern Wyoming into Montana, serves as a link between the Northern and Middle Rockies. While the massive deposition of carbonates was occurring in the Canadian and Northern Rockies from the late Precambrian to the early Mesozoic, a considerably smaller quantity of clastic sediments was accumulating in the Middle Rockies.