Political divisions of Spain

The political division of the Kingdom of Spain is based on the 8th Title of the Spanish constitution of 1978, which establishes three levels of territorial organization: municipalities, provinces and autonomous communities, the first group constituting the subdivisions of the second, and the second group constituting the subdivisions of the last. The State guarantees the realization of the principle of solidarity amongst all the constituent parts of the country.

The autonomous communities were constituted in exercise of the right to autonomy or self-government that the constitution guarantees to the nationalities and regions of Spain, while declaring the indissoluble unity of the Spanish nation. The autonomous communities constitute a highly decentralized form of territorial organization, but based on devolution, and thus Spain is not a federation, since the State is superior to the communities and retains full sovereignty. The Constitutional Court of Spain has labeled this model of territorial organization the "State of Autonomies".

The autonomous communities (comunidades autónomas in Spanish and Galician, comunitats autònomes in Catalan, autonomia erkidego in Basque) constitute the first order (highest) level of territorial organization of Spain. They were created progressively after the promulgation of the Spanish constitution in 1978, as the exercise to self-government of the "nationalities and regions" that constitute the Spanish nation. In the exercise of the right to self-government recognized in that article, autonomy was to be granted to:

The constitution allowed two exceptions to the above set of criteria, namely that the Spanish Parliament reserves the right to:

Even though the province was the basis for the creation of the autonomous communities, these roughly follow the lines of the old kingdoms and regions of the Iberian peninsula prior to unification.

...
Wikipedia