St. Stephen's & St. Agnes School (SSSAS) is an independent Episcopal coed private college preparatory school in the Seminary Ridge neighborhood of Alexandria, Virginia. The school was created from the 1991 merger of St. Agnes School (a girls' school founded in 1924) with St. Stephen's School (a boys' school founded in 1944). The school consists of three campuses within a 1.5-mile radius. The Lower School, grades JK-5, is located on Fontaine Street; the Middle School, grades 6–8, is located on Braddock Road; and the Upper School, grades 9–12, is located on St. Stephen's Road.

St. Stephen's & St. Agnes School serves students from across Northern Virginia, Maryland, and Washington, D.C. The old St. Stephen's was one of the founding schools of the Interstate Athletic Conference.