Castilian or Castillian may refer to:
- Castile, a historic region of Iberian peninsula
- Castilian people, an ethnic group from Castile
- Castilian languages, a branch of the West Iberian languages consisting of all linguistic varieties descended from Old Latin
- Spanish language, a Romance language that originated in Castile
- Crown of Castile, a former state on the Iberian Peninsula
- Kingdom of Castile, a former kingdom on the Iberian Peninsula
- Castile and León, an autonomous community of Spain
- Castile–La Mancha, an autonomous community of Spain
- SS Castilian, a 1919 British ship
- The Castilian, a 1963 film
- Castilian War, a war between several sultanates and the Spanish Empire.