The Basilica of Saint Patrick's Old Cathedral, sometimes shortened to St. Patrick's Old Cathedral or simply Old St. Patrick's, is a Catholic parish church, a basilica, and the former cathedral of the Archdiocese of New York, located in the Nolita neighborhood of Lower Manhattan, New York City. Built between 1809 and 1815 and designed by Joseph-François Mangin in the Gothic Revival style, it was the seat of the archdiocese until the current St. Patrick's Cathedral in Midtown Manhattan opened in 1879. Currently, liturgies are celebrated in English, Spanish, and Chinese. The church is at 260–264 Mulberry Street between Prince and Houston streets, with the primary entrance on Mott Street. Old St. Patrick parish merged with Most Precious Blood parish, and the two churches share priests and administrative staff.

Basilicas are Catholic church buildings that have a designation, conferring special privileges, given by the Pope. Basilicas are distinguished for ceremonial purposes from other churches. The building need not be a basilica in the architectural sense. Basilicas are either major basilicas, of which there are four, all in the Diocese of Rome, or minor basilicas, of which there were 1,810 worldwide as of 2019.