The Council of Castile (), known earlier as the Royal Council (), was a ruling body and key part of the domestic government of the Crown of Castile, second only to the monarch himself. It was established under Queen Isabella I in 1480 as the chief body dealing with administrative and judicial matters of the realm. With the 1516 ascension of King Charles I (later Holy Roman Emperor Charles V) to the throne of both Castile and Aragon, the Royal Council came to be known as the Council of Castile because Charles was king of many dominions other than Castile, while the Council retained responsibility only over Castile.