St. Ignatius College Preparatory, commonly referred to as SI, is a private, Catholic preparatory school in the Jesuit tradition, serving the San Francisco Bay Area since 1855. Located in the Archdiocese of San Francisco, in the Sunset District of San Francisco, St. Ignatius is one of the oldest secondary schools in the U.S. state of California.

The Archdiocese of San Francisco is a Latin Church ecclesiastical territory or diocese of the Catholic Church in the northern California region of the United States. The Archdiocese of San Francisco was erected on July 29, 1853, by Pope Pius IX and its cathedral is the Cathedral of Saint Mary of the Assumption.