What is Atzlan? It is the legendary ancestral home of the Aztec/Mexica. It is represented as an island in a lake, located in what is now the north of Mexico onto which the first Mexica emerged at the beginning of the fourth world.

In the origin myths of the Aztecs, they emerged originally from the bowels of the earth through seven caves (Chicomostoc) and settled in Aztlan, from which they subsequently undertook a migration southward in search of a sign that would indicate that they should settle once more. This myth roughly coincides with the known history of the Aztecs as a barbarous horde that migrated from present-day northwestern Mexico into the central plateau sometime toward the end of the first millennium AD, when high civilizations of great antiquity were already well established in the region. It is known that the Aztecs had a sector ("barrio") in the Toltec city of Tollan, and the cultural influence of the Toltecs on the rough-edged Aztecs was subsequently to be very marked. On the view of some scholars (e.g., Nigel Davies), all of Aztec cultural development was an effort to recreate the grandeur that they knew at Tollan.

The exact physical location of Aztlan is unknown, other than it must have been located near estuaries or on the coast of northwestern Mexico, though some archaeologists have gone so far as to locate the present town of San Felipe Aztlan, Nayarit, as the exact place.

In Chicano folklore, Aztlan is often appropriated as the name for that portion of Mexico that was taken over by the United States after the Mexican-American War of 1846, on the belief that this greater area represents the point of parting of the Aztec migrations. In broad interpretation, there is some truth to this in the sense that all of the groups that would subsequently become the various Nahuatl-speaking peoples of central Mexico passed through this region in a prehistoric epoch, as attested by the existence of linguistically related groups of people distributed throughout the US Pacific Intermountain region, the US southwest and northern Mexico, known as the Uto-Aztecan-Tanoan group, and including such peoples as the Paiute, Shoshoni, Hopi, Pima, Yaqui, Tepehuan, Rarámuri (Tarahumara), Kiowas and Mayas.