St. Francis de Sales Church is a Roman Catholic Oratory located in south St. Louis, Missouri, United States. It is the second largest church in the Archdiocese of St. Louis after the cathedral-basilica. The church is popularly known as the "Cathedral of South St. Louis".

A hall church is a church with a nave and aisles of approximately equal height. In England, Flanders and the Netherlands, it is covered by parallel roofs, typically, one for each vessel, whereas in Germany there is often one single immense roof. The term was invented in the mid-19th century by Wilhelm Lübke, a pioneering German art historian. In contrast to an architectural basilica, where the nave is lit from above by the clerestory, a hall church is lit by the windows of the side walls typically spanning almost the full height of the interior.