The autonomous communities exercise their right to self-government within the limits set forth in the constitution and organic laws known as Statutes of Autonomy,[ii] which broadly define the powers that they assume.

This unique framework of territorial administration has been labeled by the Constitutional Court as the "State of Autonomous Communities",[iii] to avoid implying either a unitary or federal model.

Since 2006, Occitan—in its Aranese dialect—is also a co-official language in Catalonia, making it the only autonomous community whose name has three official variants (Spanish: Cataluña, Catalan: Catalunya, Occitan: Catalonha).

The constitution of 1931 envisaged a territorial division for all Spain in "autonomous regions", which was never fully attained—only Catalonia, the Basque Country and Galicia had approved "Statutes of Autonomy"—the process being thwarted by the Spanish Civil War that broke out in 1936, and the victory of the rebel Nationalist forces under Francisco Franco.

[15] Franco's dictatorial regime strongly believed that the only way of preserving the "unity of the Spanish nation" was by ruling Spain as a highly centralized state.

The most difficult task of the newly democratically elected Cortes Generales (the Spanish Parliament) in 1977 acting as a Constituent Assembly was to transition from Franco's rigid centralism to a more decentralized model[19] in a way that would satisfy the demands of the peripheral nationalists.

Shortly after, the government allowed the creation of "assemblies of members of parliament" made up of deputies and senators of the different territories of Spain, so that they could constitute "pre-autonomic regimes" for their regions as well.

[26][28] Rather than imposing, it enables a process towards a decentralized structure based on the exercise that these "nationalities and regions" would make of the right to self-government that they were granted.

[26] As such, the outcome of this exercise was not predictable[29] and its construction was deliberately open-ended;[17] the constitution only created a process for an eventual devolution, but it was voluntary in nature: the "nationalities and regions" themselves had the option of choosing to attain self-government or not.

The "fast route" or "fast track",[27] also called the "exception",[26] was established in article 151, and was implicitly reserved for the three "historical nationalities"[28][32][33]—Catalonia, the Basque Country and Galicia, regions with strong regional identities[34]—in that the very strict requirements to opt for this route were waived for those territories that had approved a "Statute of Autonomy" during the Second Spanish Republic (1931–1936).

In terms of territorial organization, the fifth transitory disposition established that the cities of Ceuta and Melilla, Spanish exclaves located on the northern coast of Africa, could be constituted as "autonomous communities" if the absolute majority of the members of their city councils would agree on such a motion, and with the approval of the Spanish Parliament, which would exercise its prerogatives to grant autonomy to other entities besides provinces.

[26] After several months of discussion, the then prime minister of Spain, Adolfo Suárez and the leader of the opposition, Felipe González, reached an agreement to resolve the Andalusian issue, whereby the Parliament approved an amendment to the law that regulated referendums, and used a prerogative of article 144c of the constitution, both actions which combined would allow Andalusia to take the fast route.

Among other things:[26][41] In the end, 17 autonomous communities were created: Special provisions were made for the Valencian Community and the Canary Islands in that, although they took the "slow route", through the subsequent approval of specific organic laws, they were to assume full autonomy in less than 5 years, since they had started a process towards the "fast route" prior to the approval of the "autonomic pacts".

[15][28][42] The "autonomic pacts" give both Cantabria and La Rioja the option of being incorporated into Castile and León in the future, and required that the Statutes of Autonomy of all three communities include such a provision.

This has been evidenced in the 2000s, at the beginning with a wave of approval of new Statutes of Autonomy for many communities, and more recently with many considering the recentralization of some powers in the wake of the economic and financial crisis of 2008.

[45][46] By means of the State of Autonomies implemented after the Spanish Constitution of 1978, Spain has been quoted to be "remarkable for the extent of the powers peacefully devolved over the past 30 years" and "an extraordinarily decentralized country", with the central government accounting for just 18% of public spending,[47] 38% by the regional governments, 13% by the local councils, and the remaining 31% by the social security system.

In this regard, the new rules for fiscal decentralisation in force since 2011 already make Spain one of the most decentralized countries in the world also in budgetary and fiscal matters,[54] with the base for income tax split at 50/50 between the Spanish government and the regions (something unheard of in much bigger federal states such as Germany or the United States, which retain the income tax as an exclusively or primarily federal one).

In some autonomous communities, these institutions are restored historical bodies of government or representation of the previous kingdoms or regional entities within the Spanish Crown—like the Generalitat of Catalonia—while others are entirely new creations.

[67] The asymmetrical devolution is a unique characteristic of the territorial structure of Spain, in that the autonomous communities have a different range of devolved powers.

In practice these traits are a native "language proper to their own territories" separate from Spanish, a particular financial regime or special civil rights expressed in a code, which generate a distinct political personality.

[68] These hechos diferenciales of their distinct political and historical personality are constitutionally and statutorily (i. e., in their Statutes of Autonomy) recognized in the exceptions granted to some of them and the additional powers they assume.

[6] All autonomous communities have the power to manage their own finances in the way they see fit, and are responsible for the administration of education—school and universities—health and social services and cultural and urban development.

[52] That is, the central government is still charge of levying and collecting most taxes, which it then redistributes to the autonomous communities with the aim of producing "fiscal equalization".

[3] The central government is committed to returning a specific percentage of taxes to all communities with common regime, within the differences allowed for fiscal equalization.

Since they collect all taxes themselves and only send a prearranged amount to the central government for the powers exclusive to the State, they do not participate in "fiscal equalization", in that they do not receive any money back.

[6] With no legal constraints to balance budgets, and since the central government retains control over fiscal revenue in the communities of common regime, these are in a way encouraged to build up debt.

[52] The Council on Fiscal and Financial Policy, which includes representatives of the central government and of the autonomous communities, has become one of the most efficient institutions of coordination in matters of public expenditures and revenue.

[72] The preamble to the constitution explicitly stated that it is the nation's will to protect "all Spaniards and the peoples of Spain in the exercise of human rights, their cultures and traditions, languages and institutions".

[73] This is a significant recognition not only in that it differed drastically from the restrictive linguistic policies during the Franco era, but also because part of the distinctiveness of the "historical nationalities" lies on their own regional languages.

Article 3 of the constitution ends up declaring that the "richness of the distinct linguistic modalities of Spain represents a patrimony which will be the object of special respect and protection".