The Council of Aragon, officially, the Royal and Supreme Council of Aragon (Spanish: Real y Supremo Consejo de Aragón; Catalan: Consell Suprem d'Aragó) was a ruling body and key part of the domestic government of the Spanish Empire in Europe, second only to the monarch himself. It administered the Crown of Aragon, which was composed of the Kingdom of Aragon, Principality of Catalonia (including Roussillon until 1659), Kingdom of Valencia, Kingdom of Mallorca, as well as Aragon's Italian possessions (Kingdom of Sicily, Naples, and Sardinia) until the 1558 creation of the Council of Italia. The Council of Aragon ruled these territories as a part of Spain, and later the Iberian Union.
The Council of Aragon was the result of the nature of the Spanish empire, composed of individual kingdoms ruled by a common king but each retaining their own laws, customs, and government. Ferdinand II, along with his wife Isabella, was the first ruler of both Castile and Aragon. Because Ferdinand II was crowned king of Castile before becoming king of Aragon (1474 and 1479, respectively), the majority of his time was spent at the Castilian royal court in Valladolid rather than in Aragon. This royal absenteeism created problems in the government and organization for the lands of Aragon. As a result, and the viceroy and conciliar systems arose to solve these administrative problems. In 1494, the Council of Aragon was founded out of what had previously been the royal Council of the kings of Aragon. The Council consisted of a Treasurer-General, a Vice-Chancellor, and five Regentes; all of these positions except the Treasurer-General were filled with native-born Aragonese. Much of Council's members were drawn from the letrados, the lawyer-class on which Ferdinand and Isabella had relied on for administrative organization of their lands. While the viceroy remained the supreme administration in Aragon, the Council controlled their activities and was the link between the viceroy and the king. Its functions included receiving reports from viceroys, advising the king on his policies, and dispatching the king's orders to various territories. Through the Council of Aragon the king was able to oversee territories he could not visit and interact with the natives of these territories.