Roman Catholic Archdiocese of Bahía Blanca

The Roman Catholic Archdiocese of Bahía Blanca (Archidioecesis Sinus Albi) is an ecclesiastical territory or diocese of the Roman Catholic Church in the eastern region of the province of Buenos Aires, Argentina. Its mother church, located in the city of Bahía Blanca, is the Cathedral of Our Lady of Mercy. Since 10 May 2003 Guillermo José Garlatti has been its Archbishop. Since 3 November 2015, Carlos Azpiroz Costa has been its Archbishop coadjutor.

The territory of the Archdiocese covers 82,624 km² and includes a population of about 700,000 inhabitants, of which 85% (595,000 people) are Catholics, served by 57 parishes. It covers the partidos (municipalities) of Adolfo Alsina, Adolfo González Chávez, Bahía Blanca, Coronel Dorrego, Coronel de Marina Leonardo Rosales, Coronel Pringles, Coronel Suárez, Daireaux, Guaminí, Monte Hermoso, Patagones, Puán, Saavedra, San Cayetano, Tornquist, Tres Arroyos and Villarino.

The archdiocese is the head of the ecclesiastical province of Bahía Blanca, which encompasses the dioceses of all of the Provinces of Patagonia and Tierra del Fuego, and whose suffragan sees are: Diocese of Alto Valle del Río Negro, Diocese of Comodoro Rivadavia, Diocese of Río Gallegos, Diocese of San Carlos de Bariloche, Diocese of Santa Rosa, Diocese of Viedma and the Territorial Prelature of Esquel.

The diocese was erected on 20 April 1934 by Pope Pius XI's bull Nobilis Argentinae nationis, drawing from territories belonging to the Archdiocese of La Plata. Its first bishop was Leandro Bautista Astelarra (1934–1943). It was elevated to an archdiocese on 11 February 1957 by Pope Pius XII's bull Quandoquidem adoranda.