The Aché ( ah-CHAY) are an indigenous people of Paraguay. They are hunter-gatherers living in eastern Paraguay.

From the earliest Jesuit accounts of the Aché in the 17th century until their peaceful outside contacts in the 20th century, the Aché were described as nomadic hunter-gatherers living in small bands and depending entirely on wild forest resources for subsistence. In the 20th century, four different ethnolinguistic populations of Aché were contacted and pacified. They are the Northern Aché, the Yvytyruzu Aché, the Ypety Aché, and the Ñacunday Aché. Each of these populations was an endogamous dialectal group, consisting of multiple residential bands, with no peaceful interaction between the groups.

The Aché suffered repeated abuses by rural Paraguayan colonists, ranchers, and big landowners from the conquest period until the latter half of the 20th century. In the 20th century, largely under military dictator Alfredo Stroessner, the Northern Aché, who had been the only inhabitants of nearly 20,000 square kilometers of rural Paraguay, ended up confined on just two reservations totaling little more than 50 square kilometers of titled land. In the process, they were massacred, enslaved, and gathered onto reservations where no adequate medical treatment was provided. This process was specifically carried out to pacify them, and to remove them from their ancestral homeland, so that absentee investors (mainly Brazilian) could move in and develop the lands that once belonged only to the Aché. Large multinational business groups—e.g. La Industrial Paraguaya. S.A. (LIPSA)—obtained title rights to already occupied lands and then sold them sight unseen to investors, who purchased lands where Aché bands had roamed for thousands of years, and were still present. The fact that Aché inhabitants were present and living in the forests of Canindeyu and Alto Paraná on the very lands being titled in Hernandarias seems to have been dismissed by cities such as Coronel Oviedo.

The Kuetuvy Aché were forcibly removed from the Mbaracayu region in the 1970s, but managed to return to their ancestral homeland in 2000.