The purpose of this study is to investigate the inquisitorial activities of Don Fray Juan de Zumárraga, first Bishop and Archbishop of Mexico, 1528-1548. Zumárraga served as Apostolic Inquisitor in the bishopric of Mexico from 1536 to 1542, when he was superseded in that office by the Visitor General, Francisco Tello de Sandoval, largely because he had relaxed Don Carlos, the cacique of Texcoco, to the secular arm for burning, an act regarded as rash by the authorities in Spain. Throughout this essay an attempt is made to relate the Inquisition to the political and intellectual life of early sixteenth-century Mexico. Zumárraga is pictured as the defender of orthodoxy and the stabilizer of the spiritual conquest in Mexico. The relationship of the individual and of society collectively with the Holy Office of the Inquisition is stressed. With the exception of background materials, this study is based entirely upon primary sources, trial records which for the most part have lain unstudied since the sixteenth century. In all, two years of research in the Ramo de la Inquisición of the Archivo General de la Nación in Mexico City were consumed in ferreting out these materials. Subsidiary investigations in other sections of the Mexican archives were made in order to place the Inquisition materials in their proper perspective.—Richard E. Greenleaf