This article examines the language policies of sixteenth-century Mexico, aiming more generally to illuminate efforts by Mexican bishops to foster conversions to Christianity. At various points throughout the colonial era, the Spanish Crown and the Catholic Church propagated the use of Castilian among Amerindians; leaders of these institutions, however, also encouraged priests to study indigenous languages. That Spanish authorities appear to have never settled on a firm language policy has puzzled modern scholars, who have viewed the Crown and its churchmen as vacillating between “pro-indigenous” and “pro-Castilian” sentiments. This article suggests, however, that Mexico's bishops intentionally extended simultaneous support to both indigenous languages and Castilian. Church and Crown officials tended to avoid firm ideological commitments to one language; instead they made practical decisions, concluding that different contexts called for distinct languages. An examination of the decisions made by leading churchmen offers insight into how they helped to create a Spanish-American religious landscape in which both indigenous and Spanish elements co-existed.