The Altiplano (Spanish for "high plain"), Collao (Quechua and Aymara: Qullaw, meaning "place of the Qulla") or Andean Plateau is a plateau in west-central South America. Located at the latitude of the widest part of the north–south-trending Andes, it is the most extensive high plateau on Earth outside Tibet. The bulk of the Altiplano lies in Bolivia, but its northern parts lie in Peru, its southwestern fringes lie in Chile, and it extends into Argentina.

Many towns and several cities are on the plateau, including El Alto and Oruro in Bolivia and Juliaca and Puno in Peru. The northeastern part of the Altiplano is more humid than the southwestern part, which has several salares (salt flats), due to its aridity. At the Bolivia–Peru border lies Lake Titicaca, the largest lake in South America. Farther south, in Bolivia, Lake Poopó existed until recently, but by December 2015, it had completely dried up, and was declared defunct. Whether that lake, which had been the second-largest in Bolivia, can be restored is unclear.

The Altiplano was the site of several pre-Columbian cultures, including the Chiripa, Tiawanaku, and the Inca Empire. Spain conquered the region in the 16th century.

Today, major economic activities in the Altiplano include mining, llama and vicuña herding, and services (in its cities). The area also attracts some international tourism.

The Altiplano is an area of inland drainage (endorheism) lying in the central Andes, occupying parts of northern Chile, western Bolivia, southern Peru, and northwest Argentina. Its elevation averages about 3,750 meters (12,300 feet), slightly less than that of the Tibetan Plateau. Unlike conditions in Tibet, the Altiplano is dominated by massive active volcanoes of the Central Volcanic Zone to the west, such as Ampato (6288 m), Tutupaca (5,816 m), Parinacota (6348 m), Guallatiri (6071 m), Paruma (5,728 m), Uturunku (6,008 m), and Licancabur (5,916 m), and the Cordillera Real in the northeast with Illampu (6,368 m), Huayna Potosí (6,088 m), Janq'u Uma (6,427 m) and Illimani (6,438 m). The Atacama Desert, one of the driest areas on the planet, lies to the southwest of the Altiplano; to the east lies the humid Amazon rainforest.

The Altiplano is noted for hypoxic air caused by very high elevation. The communities located in the Altiplano include Qulla, Uros, Quechua, and Aymara.

Several mechanisms have been put forth for the formation of the Altiplano plateau; hypotheses try to explain why the topography in the Andes incorporates this large area of low relief at high altitude (high plateau) within the orogen:

At various times during the Pleistocene epoch, both the southern and northern Altiplano areas were covered by vast pluvial lakes. Remnants are Lake Titicaca, straddling the Peru–Bolivia border, and Poopó, a salt lake that extends south of Oruro, Bolivia. Salar de Uyuni, locally known as Salar de Tunupa, and Salar de Coipasa are two large, dry, salt flats formed after the Altiplano paleolakes dried out.