Isabelle of France (1225–1270), sister of King Louis IX of France (r. 1226–1270), is best known for rejecting marriage and founding the female Franciscan abbey of Longchamp just west of Paris. Literate in both Latin and French, Isabelle owned numerous books and was the dedicatee of at least one sophisticated Latin work of religious advice. As an author, she was the primary force behind the Rule of the Enclosed Sisters Minor, which received final papal approval in 1263 and was adopted by dozens of female communities.