Castilianization or Castilianisation (Spanish: castellanización), also referred to as Hispanization, is a term used to describe a cultural change in which something or someone non-Castilian (that is Spanish) becomes (voluntarily or by force) Spanish.
The term is often used in relation to minority languages of Spain such as the Catalan language, which are threatened not only because of language shift but because of progressive linguistic assimilation due to typological similitude (e.g. Catalan no longer creates new vocabulary or slang on its own, merely copying Spanish forms). It is also used to refer to the imposition of the Spanish language in the former Spanish colonies such as Mexico and its adoption by indigenous peoples. Until recently, castilianization has been official policy by the governments of many Latin American countries. Only recently programs of intercultural bilingual education have been introduced to a substantial extent.