Quechua (Quechua, Runa Simi) is an American Indian language native to South America and related to Aymará, both members of the Quechumaran linguistic stock. It was the official language of the Tahuantinsuyu (Inca empire), and today is spoken in various dialects by some 9.6 million people throughout South America. The language's dominion spans the entire South American continent starting as far north as southern Colombia and Ecuador, Peru and Bolivia, and northwestern Argentina and northern Chile. The dialect as it is spoken in Colombia and Ecuador is known as Quichua (Quichua, Runa Shimi), and because of its frequent unintelligibility with the main branch of the language, it borders on being classed as a separate language. Despite this, all dialects are nonetheless considered a single tongue, consequently making it the most widely spoken of all American Indian languages in the Americas.

The language was extended beyond the limits of the empire by the Catholic Church, which chose it to preach to Indians in the Andes area. It has, along with Spanish and Aymará, the status of an official language in both Peru and Bolivia. Before the arrival of the Spaniards and the introduction of the Latin alphabet, Quechua had no written alphabet, instead, it had a system of accountance with khipu-strings.

Quechua is a very regular language, but a large number of infixes and suffixes change both the overall significance of words and their subtle shades of meaning, allowing great expressiveness. It includes grammatical features such as bipersonal conjugation and conjugation dependent on mental state and veracity of knowledge, spatial and temporal relationships, and many cultural factors.