The Ancestral Puebloans, also known as Ancestral Pueblo peoples or the Basketmaker-Pueblo culture, were an ancient Native American culture of Pueblo peoples spanning the present-day Four Corners region of the United States, comprising southeastern Utah, northeastern Arizona, northwestern New Mexico, and southwestern Colorado. They are believed to have developed, at least in part, from the Oshara tradition, which developed from the Picosa culture.

The Ancestral Puebloans lived in a range of structures that included small family pit houses, larger structures to house clans, grand pueblos, and cliff-sited dwellings for defense. They had a complex network linking hundreds of communities and population centers across the Colorado Plateau. They held a distinct knowledge of celestial sciences that found form in their architecture. The kiva, a congregational space that was used mostly for ceremonies, was an integral part of the community structure.

Archaeologists continue to debate when this distinct culture emerged. The current agreement, based on terminology defined by the Pecos Classification, suggests their emergence around the 12th century BCE, during the archaeologically designated Early Basketmaker II Era. Beginning with the earliest explorations and excavations, researchers identified Ancestral Puebloans as the forerunners of contemporary Pueblo peoples. Three UNESCO World Heritage Sites located in the United States are credited to the Pueblos: Mesa Verde National Park, Chaco Culture National Historical Park and Taos Pueblo.

Pueblo, which means "village" and "people" in Spanish, was a term originating with the Spanish explorers who used it to refer to the people's particular style of dwelling. The Navajo people, who now reside in parts of former Pueblo territory, referred to the ancient people as Anaasází in their Diné language, an exonym meaning "ancestors of our enemies", referring to their competition with the Pueblo peoples. The Navajo now use the term in the sense of referring to "ancient people" or "primitive ones", i.e., savages or barbarians, whereas others ascribe the meaning of Anasazi to "the older ones who are different from our people"; (lit. Ana = "different from us" + asaza = "the old ones"). In the twentieth century, the people and their archaeological culture were often referred to by the Diné exonym. Alfred V. Kidder, who mistakenly thought it was Diné for old people, used the term in the 1927 Pecos Classification system. Contemporary Pueblos view this term as derogatory and object to the use of the term. Modern descendants of this culture often choose to use the term Ancestral Pueblo peoples. Hopi people use the term Hisatsinom, meaning "ancient people", to describe the Ancestral Puebloans. Archaeologist Linda S. Cordell discussed the word's etymology and use:

The name "Anasazi" has come to mean "ancient people," although the word itself is Navajo, meaning "enemy ancestors." [The Navajo word is anaasází (< anaa- "enemy", sází "ancestor").] It is unfortunate that a non-Pueblo word has come to stand for a tradition that is certainly ancestral Pueblo. The term was first applied to ruins of the Mesa Verde by Richard Wetherill, a rancher and trader who, in 1888–1889, was the first Anglo-American to explore the sites in that area. Wetherill knew and worked with Navajos and understood what the word meant. The name was further sanctioned in archaeology when it was adopted by Alfred V. Kidder, the acknowledged dean of Southwestern Archaeology. Kidder felt that it was less cumbersome than a more technical term he might have used. Subsequently some archaeologists who would try to change the term have worried that because the Pueblos speak different languages, there are different words for "ancestor," and using one might be offensive to people speaking other languages.

Others have objected to Cordell's definition of the name "Anasazi", saying that its true connotation means in the Navajo language "those that do things differently." In yet another account, the term Anasazi originated from a Navajo adoption of a Ute word that literally means "ancient enemy" or "primitive enemy", but was used by the Navajo to mean "savage" or "barbarian", hence the Pueblos' rejection of the term.^{[citation needed]}

The Ancestral Puebloans were one of four major prehistoric archaeological traditions recognized in the American Southwest, also known as Oasisamerica. The others are the Mogollon, Hohokam, and Patayan. In relation to neighboring cultures, the Ancestral Puebloans occupied the northeast quadrant of the area. The Ancestral Pueblo homeland centers on the Colorado Plateau, but extends from central New Mexico on the east to southern Nevada on the west.

Areas of southern Nevada, Utah, and Colorado form a loose northern boundary, while the southern edge is defined by the Colorado and Little Colorado Rivers in Arizona and the Rio Puerco and Rio Grande in New Mexico. Structures and other evidence of Ancestral Puebloan culture have been found extending east onto the American Great Plains, in areas near the Cimarron and Pecos Rivers and in the Galisteo Basin.