According to its Constitution, Castilian (Spanish) is the official language throughout Spain, without prejudice to the official status of other languages in specific regions of the country.

The statutes of autonomy have established the following official languages in their respective territories: Catalan (Català) in Catalonia and the Balearic Islands, Valencian (Valencià) in the Valencian Community, Galician (Galego) in Galicia, Basque (Euskara) in the Basque Country and part of Navarre, and Aranese (Aranès) in Catalonia.

Catalan and Valencian are considered two varieties of the same language.

The term "Castellano" originates from the region of Castile, where the language developed. In Spain, "Castellano" can be used to refer to the country’s official language or specifically to the dialect spoken in Castile. In other regions, "Spanish" is used to refer to the official language.