Joseph Sadoc Alemany (1814 - 1888) was a U.S. (Spanish-born) Roman Catholic archbishop and missionary. He served as the first Bishop of Monterey from 1850 until 1853, and the first Archbishop of San Francisco from 1853 until 1884.

Born in Vic, Catalonia, Alemany entered the Dominican Order. He was ordained a priest in 1837 and consecrated as Bishop of Monterey in 1850. When the Roman Catholic Archdiocese of San Francisco was erected in 1853, Alemany was appointed as its first archbishop. Prior to becoming a bishop, Alemany had spent a decade engaged in missionary activity in the United States, eventually becoming a naturalized American citizen.

As Archbishop of San Francisco, Alemany presided over what became a multinational diocese, owing to the influx of people during the California Gold Rush, and parishes were established for San Francisco's Italian, Irish, French and Mexican communities. Catholic religious orders were also active during his tenure, with the Society of Jesus establishing Santa Clara University and the University of San Francisco, the De La Salle Christian Brothers taking over the diocesan Saint Mary's College, and the Sisters of Notre Dame de Namur establishing the College of Notre Dame .

The scope of his authority was large, as the Diocese of Monterey originally encompassed the entire state of California, while the Archdiocese of San Francisco encompassed all of California north of Monterey. However, Alemany wished to return to missionary work and requested a coadjutor bishop. In 1883, Bishop Patrick Riordan was appointed coadjutor, and would succeed Alemany upon the latter's resignation as archbishop in 1884.

After his resignation, Alemany returned to Spain and was appointed titular archbishop of Pelusium. Alemany died in Valencia, Spain in 1888.