Ethnohistory reads colonial era chronicles, indigenous codices, mission records and legal documents together, treating each as a partial and interested account of Mesoamerican society to be checked against the others and against archaeology, rather than treating the Spanish colonial record as neutral fact. The method gained its first dedicated professional home in 1954, when the American Society for Ethnohistory was founded, growing out of the Ohio Valley Historic Indian Conference, and began publishing the journal Ethnohistory the same year, giving historians working with native testimony a venue distinct from either conventional archival history or archaeology alone.
Aztec, Maya and other Mesoamerican religious practice survives today mainly through colonial Spanish description, often written by missionaries with an explicit interest in condemning what they described, alongside a smaller body of surviving indigenous pictorial and alphabetic testimony. Mesoamerican ethnohistory is what lets the atlas weigh a colonial friar's account of a ritual against surviving native sources and archaeological evidence for the same practice, rather than repeating the colonial account as though it were disinterested reporting.