Castilian may refer to:
- Alternative name for the Spanish language (For details, see: names given to the Spanish language).
- Something related to the Crown of Castile, a former state in present-day Spain
- Something related to the Kingdom of Castile, a former kingdom around which the Crown of Castile was formed
- Something related to Castile and León, an autonomous community in Spain
- Something related to Castile–La Mancha, an autonomous community in Spain
- Something related to Castile (historical region), in Spain
- Castilian people, the ethnic group from this region
- Castilian Spanish, a variety of the Spanish language spoken in central and northern Spain (see Spanish dialects and varieties for a more general view)