Although ninety per cent of the documentation of the Mexican Holy Office of the Inquisition is to be found in the Archivo General de la Nación in Mexico City, a critical group of manuscripts must be consulted in Spain if the researcher is to study the Mexican institution effectively. These records are contained in the archive of the Consejo de la Suprema y General Inquisición and in the plethora of royal documents emanating from and arriving in the Council of the Indies. Unfortunately the manuscripts are scattered among the three great archives in the Iberian peninsula: Archivo de Simancas at Valladolid, Archivo Histórico Nacional in Madrid, and Archivo General de Indias in Sevilla. The Simancas and Sevilla documents on the Mexican Inquisition are relatively sparse; but the AHN houses the extant archive of the Suprema and is a required visit for any investigator in Mexican Inquisition materials from 1571 to 1820.