The Codex Calixtinus (also Compostellus) is the main witness for the 12th-century Liber Sancti Jacobi, or the Book of Saint James. It is a pseudepigraph attributed to Pope Callixtus II; its principal author or compilator is referred to as "Pseudo-Callixtus", often identified with French scholar Aymeric Picaud. Its most likely date of compilation is the period of 1138–1145.