The Iberian Union is the dynastic union of the Crown of Portugal and the Spanish Crown between 1580 and 1640, bringing the entire Iberian Peninsula, as well as Spanish and Portuguese overseas possessions, under the Spanish Habsburg kings Philip II, Philip III and Philip IV of Spain.

The union begins as a result of the Portuguese crisis of succession and the ensuing War of the Portuguese Succession and lasts sixty years, until the Portuguese Restoration War in which the House of Braganza is established as Portugal's new ruling dynasty.

The Habsburg king is the only element of connection between the multiple kingdoms and territories, who rules by six separate government councils of Castile, Aragon, Portugal, Italy, Flanders and the Indies.

The governments, institutions, and legal traditions of each kingdom remains independent of each other.

Alien laws (Leyes de extranjeria) determine that the national of one kingdom is a foreigner in all the other Iberian kingdoms.