The Wichí are an indigenous people of South America. They comprise a large group of tribes inhabiting the headwaters of the Bermejo and Pilcomayo rivers in Argentina and Bolivia.

This ethnic group was referred to by English settlers as Mataco, a term that is still widely used. The etymology of this term is obscure; however, several sources note that the Wichí consider it derogatory. Among the Wichí, a folk etymology relates the term to the Spanish verb matar ("to kill").

Their preferred self-designation is Wichí, meaning "people" (Wichí Lhamtés Güisnay pronunciation: [wiˈkʲi]), and their language is known as Wichí Lhamtés ([wikʲi l̥amˈtes]).

In some areas of Bolivia, there is a pronunciation variant [wikˠiʡ], and the group refers to themselves as Weenhayek Wichí, translated by Alvarsson (1988) as "the different people" (plural: Weenhayey). According to Weenhayey informants interviewed by Alvarsson, the original name was Olhamelh ([oɬameɬ]), meaning simply "us."

Subgroups within the Wichí have been identified and referred to by different names in the literature: Nocten or Octenay in Bolivia; Véjos, more properly Wejwus or Wehwos, for the western subgroup(s); and Güisnay for the eastern subgroups in Argentina. The latter corresponds to Tewoq-lhelej, meaning "the river people."

At present, various Wichí groups can be found in Argentina and Bolivia, distributed as follows:

Argentina:

Bolivia: