Uto-Aztecan, Uto-Aztekan or (rarely in English) Uto-Nahuatl is a family of indigenous languages of the Americas, consisting of over thirty languages. Uto-Aztecan languages are found almost entirely in the Western United States and Mexico. The name of the language family was created to show that it includes both the Ute language of Utah and the Nahuan languages (also known as Aztecan) of Mexico.

The Uto-Aztecan language family is one of the largest linguistic families in the Americas in terms of number of speakers, number of languages, and geographic extension. The northernmost Uto-Aztecan language is Shoshoni, which is spoken as far north as Salmon, Idaho, while the southernmost is the Pipil language of El Salvador and Nicaragua. Ethnologue gives the total number of languages in the family as 61, and the total number of speakers as 1,900,412. Speakers of Nahuatl languages account for over 85% of these.

The internal classification of the family often divides it into two branches: a northern branch including all the languages of the US and a southern branch including all the languages of Mexico, although it is still being discussed whether this is best understood as a genetic classification or as a geographical one. Below this level of classification the main branches are well accepted: Numic (including languages such as Comanche and Shoshoni) and the Californian languages (formerly known as the Takic group, including Cahuilla and Luiseño) account for most of the Northern languages. Hopi and Tübatulabal are languages outside those groups. The Southern languages are divided into the Tepiman languages (including O'odham and Tepehuán), the Tarahumaran languages (including Raramuri and Guarijio), the Cahitan languages (including Yaqui and Mayo), the Coracholan languages (including Cora and Huichol), and the Nahuan languages.

The homeland of the Uto-Aztecan languages is generally considered to have been in the Southwestern United States or possibly Northwestern Mexico. An alternative theory has proposed the possibility that the language family originated in southern Mexico, within the Mesoamerican language area, but this has not been generally considered convincing.