Identification. The Ache are a South American native population of hunter-gatherers that has lived in eastern Paraguay since at least the first Jesuit missionary reports in the 1600s. They were referred to as "Guayaki" in historic and ethnographic reports before the 1960s, when the first currently living bands were contacted. Because they refer to themselves as "Ache," this label has been adopted in most subsequent ethnographic reports.
Location. In the seventeenth and eighteenth centuries the Ache apparently roamed much of the forest in eastern Paraguay between the Guaira waterfall on the upper Paraná River, to just north of the present-day city of Encarnación. They were concentrated particularly in the low mountain ranges stretching from the Cordilla de San Rafael in the south to the Mbaracayu range in the north, and along the right bank of the middle stretches of the Paraná River. In the twentieth century, four major groupings of Ache ranged from the Ñacunday River and the Yvytyruzu foothills in the south to the Mbaracayu range in the north.
Demography. Four groupings of Ache were contacted in the second half of the twentieth century. These groups are designated by the regions they occupied at contact and the respective populations at contact can be estimated as follows: Northern Ache, about 650 individuals; Yvytyruzu Ache, about 60 individuals; Ypety Ache, about 40 individuals; Ñacunday Ache, 28 individuals. A census in 1987 resulted in the following population count: Northern Ache, 459 individuals; Yvytyruzu Ache, 87 individuals; Ypety Ache 30 individuals; Ñacunday Ache, 38 individuals. Informant accounts indicate that the Northern Ache and the Yvytyruzu Ache were a single group until the early 1930s, when they split up and never saw each other again.
Linguistic Affiliation. The Ache language is classified in the Tupí-Guaraní Linguistic Family. Each of the four independent groups speaks a different dialect, with the Northern and Yvytyruzu Ache dialects being very close, the Ypety group intermediate, and the Ñacunday dialect showing greatest divergence from the others. The Ache language is similar in many respects to the Guaraní spoken by other native groups of Paraguay, but it differs considerably in pronunciation and in the lack of verb-stem conjugations. Ache and currently spoken Guaraní are mutually unintelligible, and about as similar as Spanish and Italian.