The Crown of Aragon is a composite monarchy, also referred to as a confederation of individual polities or kingdoms ruled by one king with a personal and dynastic union of the Kingdom of Aragon and the county of Barcelona.

At the height of its power in the 14th and 15th centuries, the Crown of Aragon is a thalassocracy (a state with primarily maritime realms) controlling a large portion of the present-day eastern Spain and southwestern France, as well as some of the major islands and mainland possessions stretching across the Mediterranean as far as Greece.

The component realms of the Crown are not united politically except at the level of the king, who rules over each autonomous polity according to its own laws, raising funds under each tax structure, dealing separately with each cortes.

Put in contemporary terms, the disparate lands of Aragon function more as a confederacy of cultures rather than as a single country.

In this sense, the larger Crown of Aragon must not be confused with one of its constituent parts, the Kingdom of Aragon, from which it takes its name.In 1469, a new dynastic familial union of the Crown of Aragon with the Crown of Castile by the Catholic Monarchs, joining what contemporaries refer to as "the Spains" leads to what will become the Kingdom of Spain under King Philip II.

The Crown exists until it is abolished by the Nueva Planta decrees issued by King Philip V in 1716 as a consequence of the defeat of Archduke Charles in the War of the Spanish Succession.