The Diocese of San Diego is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Southern California, United States. Its ecclesiastical territory includes all of San Diego and Imperial Counties.

The Archdiocese of Los Angeles is a Latin Church ecclesiastical territory or archdiocese of the Catholic Church located in the southern portion of the U.S. state of California. The archdiocese's cathedra is in Los Angeles, the archdiocese comprises the California counties of Los Angeles, Santa Barbara and Ventura. The cathedral is the Cathedral of Our Lady of the Angels in Los Angeles, and its present archbishop is José Horacio Gómez Velasco. With over five million professing members and weekly liturgies celebrated in 32 languages, the Archdiocese of Los Angeles is numerically the single largest and most ethnically diverse archdiocese in the United States.