The text, given as a charged paper at the Conreso de Historia de la Corona de Aragon, starts with a critical survey of traditional and recent historiography on the institutional structure of the Crown of Aragon. It's focused on the concepts of "pluralismo coordinado" (Lalinde Abadia) and of "composite monarchy" (Elliot, Koenigsberger), revealing strenghts and the weaknesses of the supernational state in the late Middle Ages. Each kingdom of the whole monarchy is then analysed in its institutional history and in its relationship with the central monarchy.