Guarani are a group of culturally-related indigenous peoples of South America. They are distinguished from the related Tupi by their use of the Guarani language. The traditional range of the Guarani people is in present-day Paraguay between the Paraná River and lower Paraguay River, the Misiones Province of Argentina, southern Brazil once as far east as Rio de Janeiro, and parts of Uruguay and Bolivia.

Although their demographic dominance of the region has been reduced by European colonisation and the commensurate rise of mestizos, there are contemporary Guarani populations in these areas. Most notably, the Guarani language, still widely spoken across traditional Guarani homelands, is one of the two official languages in Paraguay, the other one being Spanish. The language was once looked down upon by the upper and middle classes, but it is now often regarded with pride and serves as a symbol of national distinctiveness. The Paraguayan population learns Guarani both informally from social interaction and formally in public schools. In modern Spanish, Guarani also refers to any Paraguayan national in the same way that the French are sometimes called Gauls.