Monument Valley (Navajo: Tsé Biiʼ Ndzisgaii, meaning valley of the rocks) is a region of the Colorado Plateau characterized by a cluster of vast sandstone buttes, the largest reaching 1,000 ft (300 m) above the valley floor. It is located on the Arizona-Utah state line (around 36°59′N 110°6′W), near the Four Corners area. The valley lies within the range of the Navajo Nation Reservation, and is accessible from U.S. Highway 163.

Director John Ford used the location for a number of his best known films, and thus, in the words of critic Keith Phipps, "its five square miles have defined what decades of moviegoers think of when they imagine the American West."

The area is part of the Colorado Plateau. The elevation of the valley floor ranges from 5,000 to 6,000 feet above sea level. The floor is largely siltstone of the Cutler Group, or sand derived from it, deposited by the meandering rivers that carved the valley. The valley's vivid red color comes from iron oxide exposed in the weathered siltstone. The darker, blue-gray rocks in the valley get their color from manganese oxide.

The buttes are clearly stratified, with three principal layers. The lowest layer is the Organ Rock Shale, the middle is de Chelly Sandstone, and the top layer is the Moenkopi Formation capped by Shinarump Conglomerate. The valley includes large stone structures including the famed Eye of the Sun.

Between 1948 and 1967, the southern extent of the Monument Upwarp was mined for uranium, which occurs in scattered areas of the Shinarump Conglomerate; vanadium and copper are associated with uranium in some deposits (see Uranium mining in Arizona).

Monument Valley is officially a large area that includes much of the area surrounding Monument Valley Navajo Tribal Park, a Navajo Nation equivalent to a national park. Oljato, for example, is also within the area designated as Monument Valley.

Visitors may pay an access fee and drive through the park on a 17-mile (27 km) dirt road (a 2-3 hour trip). Tours are also available, and the fee varies between about $40 and $100 per person depending on the services provided and route. Parts of Monument Valley are accessible only by guided tour, such as Mystery Valley and Hunts Mesa.

Horse rides are also available from various establishments both inside the park and in the general Monument Valley area, and rates vary widely depending on the length of the ride. Rides may be only an hour, or overnight camping trips. Additionally, hot air balloon flights are available May 1 through October 31, and small airplane flights are sometimes available.

Monument Valley is part of the Grand Circle, which includes the Grand Canyon National Park, Mesa Verde National Park, Bryce Canyon National Park, Zion National Park, Capitol Reef National Park, Canyonlands National Park, Natural Bridges National Monument, Hovenweep National Monument, Arches National Park and many other attractions.