St. Louis University High School (SLUH) is an all-male Jesuit high school in St. Louis, Missouri. Founded in 1818, it is the oldest secondary educational institution in the United States west of the Mississippi River, and one of the largest private high schools in Missouri. It is located in the Archdiocese of St. Louis.

The Archdiocese of St. Louis is a Latin Church ecclesiastical territory or archdiocese of the Catholic Church that covers the City of St. Louis and the Missouri counties of Franklin, Jefferson, Lincoln, Perry, Saint Charles, Saint Francois, Ste. Genevieve, St. Louis, Warren, and Washington. It is the metropolitan see of the ecclesiastical province containing three suffragan sees: Diocese of Springfield-Cape Girardeau, the Diocese of Jefferson City, and the Diocese of Kansas City-Saint Joseph. It is led by Archbishop, Mitchell Thomas Rozanski, formerly the Bishop of Springfield in Massachusetts.