St. Mary's Basilica – officially The Church of the Immaculate Conception of the Blessed Virgin Mary – is a church of the Diocese of Phoenix located at 231 North 3rd Street at the corner of East Monroe Street in downtown Phoenix, Arizona. It was previously known as St. Mary's Church. It was built from 1902 to 1914 in a combination of the Mission Revival and Spanish Colonial Revival styles, and was dedicated in 1915. It replaced an earlier adobe church built in 1881 when the parish was founded. From 1895 the parish was staffed by the Franciscan Friars, but it is currently staffed and operated by clergy of the Diocese of Phoenix. The current church was elevated to a minor basilica by Pope John Paul II in 1985.

The Diocese of Phoenix is a Latin Church ecclesiastical territory, or diocese, in western and central Arizona in the United States. It is a suffragan diocese of the ecclesiastical province of the Archdiocese of Santa Fe.