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.

Los Angeles, often referred to by its initials L.A., is the most populous city in the U.S. state of California. With roughly 3.9 million residents within the city limits as of 2020, Los Angeles is the second-most populous city in the United States, behind only New York City; it is also the commercial, financial and cultural center of Southern California. Los Angeles has an ethnically and culturally diverse population, and is the principal city of a metropolitan area of 13.2 million people. Greater Los Angeles, which includes the Los Angeles and Riverside–San Bernardino metropolitan areas, is a sprawling metropolis of over 18 million residents.