The Theologia Indorum ("Theology for the Indians" or "Theology of the Indians") was written by the Spanish Dominican friar Domingo de Vico from 1552-1554. It is considered the first original Christian theology written in the Americas and the longest single text written in an indigenous language of the Americas in the colonial era. Written in K'iche' (sometimes written as "Quiché,") a Mayan language of Guatemala, it played a major role in Spanish efforts to convert the Highland Maya.

The library has 10 volumes of grammars, vocabularies, sermons, and other religious writings in the Kaqchikel and K'iche' languages of Guatemala. Several have been studied, notably by Daniel G. Brinton in APS Proceedings 21 (1884): 345, and Nora B. Thompson, "Algunos manuscritos guatemaltecos en Filadelfia", Anales de la Sociedad de Geografia e Historia 23 (1948), Nos. 1 2: p. 3; and all have been described by John F. Freeman, "Manuscript Sources on Latin American Indians," APS Proceedings 10 (1962): 530, and in Freeman's Guide to Manuscripts relating to the American Indian (1966).