Quechua (/ˈkɛtʃuə/, Spanish: [ˈketʃwa]), also called Runa simi (Quechua: [ˈɾʊna ˈsɪmɪ], 'people's language') in Southern Quechua, is an indigenous language family that originated in central Peru and thereafter spread to other countries of the Andes. Derived from a common ancestral "Proto-Quechua" language, it is the most widely spoken pre-Columbian language family of the Americas, with an estimated 8–10 million speakers in 2004, and just under 7 million from the most recent census data available up to 2011. Approximately 13.9% (3.7 million) of Peruvians speak a Quechua language.

Although Quechua began expanding many centuries before the Incas, that previous expansion also meant that it was the primary language family within the Inca Empire. The Spanish tolerated its use until the Peruvian struggle for independence in the 1780s. As a result, various Quechua languages are still widely spoken, being the majority language in a number of regions of Peru, the most-spoken or co-official language in many others, and, as the Kichwa language, the second most-spoken language of Ecuador, after Spanish.

The Quechua linguistic homeland may have been Central Peru. It has been speculated that it may have been used in the Chavín and Wari civilizations.

Quechua had already expanded across wide ranges of the central Andes long before the expansion of the Inca Empire. The Inca were one among many peoples in present-day Peru who already spoke a form of Quechua, which in the Cuzco region particularly has been heavily influenced by Aymara, hence some of the characteristics that still distinguish the Cuzco form of Quechua today. Diverse Quechua regional dialects and languages had already developed in different areas, influenced by local languages, before the Inca Empire expanded and further promoted Quechua as the official language of the Empire.

After the Spanish conquest of Peru in the 16th century, Quechua continued to be used widely by the indigenous peoples as the "common language". It was officially recognized by the Spanish administration, and many Spaniards learned it in order to communicate with local peoples. The clergy of the Catholic Church adopted Quechua to use as the language of evangelization. The oldest written records of the language are by missionary Domingo de Santo Tomás, who arrived in Peru in 1538 and learned the language from 1540. He published his Grammatica o arte de la lengua general de los indios de los reynos del Perú (Grammar or Art of the General Language of the Indians of the Kingdoms of Peru) in 1560. Given its use by the Catholic missionaries, the range of Quechua continued to expand in some areas.

In the late 18th century, colonial officials ended the administrative and religious use of Quechua. They banned it from public use in Peru after the Túpac Amaru II rebellion of indigenous peoples. The Crown banned "loyal" pro-Catholic texts in Quechua, such as Garcilaso de la Vega's Comentarios Reales.

Despite a brief revival of the language immediately after the Latin American nations achieved independence in the 19th century, the prestige of Quechua had decreased sharply. Gradually its use declined so that it was spoken mostly by indigenous people in the more isolated and conservative rural areas. Nevertheless, in the 21st century, Quechua language speakers number roughly 7 million people across South America, more than any other indigenous language family in the Americas.

As a result of Inca expansion into Central Chile, there were bilingual Quechua-Mapudungu Mapuche in Central Chile at the time of the Spanish arrival. It has been argued that Mapuche, Quechua, and Spanish coexisted in Central Chile, with significant bilingualism, during the 17th century. Alongside Mapudungun, Quechua is the indigenous language that has influenced Chilean Spanish the most.