Machu Picchu, also spelled Machupijchu, site of ancient Inca ruins located about 80 k northwest of Cusco, Peru, in the Cordillera de Vilcabamba of the Andes Mountains on a 2,430-metre mountain ridge. In the Quechua language, Machu means "old" or "old person", while pikchu means either "portion of coca being chewed" or "pyramid, pointed multi-sided solid; cone". Thus the name of the site is sometimes interpreted as "old mountain".

It is perched above the Urubamba River valley in a narrow saddle between two sharp peaks—Machu Picchu and Huayna Picchu (“New Peak”)—at an elevation of 2,350 metres. One of the few major pre-Columbian ruins found nearly intact, Machu Picchu was designated a UNESCO World Heritage site in 1983.

Most archaeologists believe that Machu Picchu was constructed as an estate for the Inca emperor Pachacuti (1438–1472). Often mistakenly referred to as the "Lost City of the Incas", it is the most familiar icon of Inca civilization. The Incas built the estate around 1450 but abandoned it a century later at the time of the Spanish conquest. Although known locally, it was not known to the Spanish during the colonial period and remained unknown to the outside world until American historian Yale University professor Hiram Bingham brought it to international attention in 1911.

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 tourists a better idea of how they originally appeared. By 1976, 30% of Machu Picchu had been restored and restoration continues.

The dwellings at Machu Picchu were probably built and occupied from the mid-15th to the early or mid-16th century. Machu Picchu’s construction style and other evidence suggest that it was a palace complex of the ruler Pachacuti Inca Yupanqui (reigned c. 1438–71). Several dozen skeletons were excavated there in 1912, and, because most of those were initially identified as female, Bingham suggested that Machu Picchu was a sanctuary for the Virgins of the Sun (the Chosen Women), an elite Inca group. Technology at the turn of the 21st-century, however, identified a significant proportion of males and a great diversity in physical types. Both skeletal and material remains now suggest to scholars that Machu Picchu served as a royal retreat. The reason for the site’s abandonment is also unknown, but lack of water may have been a factor.

The high level of preservation and the general layout of the ruin are remarkable. Its southern, eastern, and western portions are surrounded by dozens of stepped agricultural terraces formerly watered by an aqueduct system. Some of those terraces were still being used by local Indians when Bingham arrived in 1911. Walkways and thousands of steps, consisting of stone blocks as well as footholds carved into the underlying rock, connect the plazas, the residential areas, the terraces, the cemetery, and the major buildings. The Main Plaza, partly divided by wide terraces, is at the north-central end of the site. At the southeastern end is the only formal entrance, which leads to the Inca Trail.

Machu Picchu is a UNESCO World Heritage Site since 1983 and designated one of the New Seven Wonders of the World in 2007, Machu Picchu is Peru’s most visited attraction and South America’s most famous ruins, welcoming hundreds of thousands of people a year. Increased tourism, the development of nearby towns, and environmental degradation continue to take their toll on the site, which is also home to several endangered species. As a result, the Peruvian government has taken steps to protect the ruins and prevent erosion of the mountainside in recent years.