The Principia is an educational institution for Christian Scientists located on two campuses in the St. Louis, Missouri metropolitan area of the United States. Principia School, located in Town and Country, West St. Louis County, serves students from early childhood through high school, and Principia College, located about thirty miles away, is on the bluffs overlooking the Mississippi River in Elsah, Illinois.

Town and Country is a city in west St. Louis County, Missouri, United States with a population of 11,640 as of the 2020 census. It is home to Missouri Baptist Medical Center,.