The military-religious Order of Santiago was founded in the last third of the XII century in the kingdom of León for the purpose of fighting Spanish Muslims. For this reason, its territorial, political and economic growth is associated to the Reconquest of the Iberian Peninsula. One of the outstanding members of the Order was Enrique de Trastámara, son of Fernando I of Aragon, who was appointed grand master, the highest authority of the institution, when he was only 9 years old and would be in the post until his death. His most important legacy was the General Chapter held in the Monastery of Uclés in 1440, where the new rules of the Order were established. This book, which belonged to Diego Fernandez de Córdoba, is probably one of the first copies of these “Establecimientos”. Orden de Santiago.