Machu Picchu is a 15th-century Inca citadel located in the Eastern Cordillera of southern Peru on a 2,430-meter (7,970 ft) mountain ridge. Often referred to as the "Lost City of the Incas", it is the most familiar icon of the Inca Empire. It is located in the Machupicchu District within Urubamba Province above the Sacred Valley, which is 80 kilometers (50 mi) northwest of Cusco. The Urubamba River flows past it, cutting through the Cordillera and creating a canyon with a tropical mountain climate.

For most speakers of English or Spanish, the first 'c' in Picchu is silent. In English, the name is pronounced or , in Spanish as [ˈmatʃu ˈpitʃu] or [ˈmatʃu ˈpiktʃu], and in Quechua (Machu Pikchu) as [ˈmatʃʊ ˈpɪktʃʊ].

The Inca civilization had no written language and no European visited the site until the 19th century, so far as is known, so there are no written records of the site while it was in use. The names of the buildings, their supposed uses, and their inhabitants are the product of modern archaeologists on the basis of physical evidence, including tombs at the site.

Most recent archaeologists believe that Machu Picchu was constructed as an estate for the Inca emperor Pachacuti (1438–1472). The Incas built the estate around 1450 but abandoned it a century later, at the time of the Spanish conquest. According to the new AMS radiocarbon dating, it was occupied from c. 1420–1532. Historical research published in 2022 claims that the site was probably called Huayna Picchu by the Inca, as it exists on the smaller peak of the same name.

Machu Picchu was built in the classical Inca style, with polished dry-stone walls. Its three primary structures are the Intihuatana, the Temple of the Sun, and the Room of the Three Windows. Most of the outlying buildings have been reconstructed in order to give visitors a better idea of how they originally appeared. By 1976, 30% of Machu Picchu had been restored and restoration continues.

Machu Picchu was declared a Peruvian Historic Sanctuary in 1981 and a UNESCO World Heritage Site in 1983. In 2007, Machu Picchu was voted one of the New Seven Wonders of the World in a worldwide internet poll.