Castilian is a noun and adjective that refers to the region and former kingdom of Castile in Spain; in particular, it refers to the language of this region, and is therefore considered by many to be a synonym of Spanish, though with different nuances. Please refer to the following articles for further information.

• Castile, for information on the region and its people.
• Spanish language, for general information on the language including dialectal variation in Castile, the rest of Spain and Spain's former colonies.
• Names given to the Spanish language, for details on the use of the terms español, castellano, Spanish and Castilian.