Spanish is the only official and preponderant language throughout the territory. A large part of the “Route of the Castilian language” passes through the autonomous community, which indicates the importance traditionally attributed to this land in the origin and subsequent development of that language. In the province of Burgos begins its journey, due both to being the birthplace of the language according to Ramón Menéndez Pidal, and the famous Cantar de Mio Cid. Valladolid stands out for having been the residence of the author of Don Quixote, Miguel de Cervantes, as well as authors such as José Zorrilla or Miguel Delibes and the thrust of its University.

Regarding the first testimonies of the Castilian language, in the Abbey of Santo Domingo de Silos a very old beatus, the Silos Beatus is preserved. The Glosas Silenses come from that Monastery. Also in Castilian lands is the Monastery of San Pedro de Cardeña, place where the Cardeña Beatus was written. In addition, the Statute of Autonomy of the community itself mentions the Cartularies of Valpuesta and the Nodicia de kesos as the most primitive traces of Castilian (Spanish) language. The Instituto Castellano y Leonés de la Lengua is responsible for carrying out various scientific works in this regard.

In addition to the Castilian language, in Castile and León two other languages or linguistic varieties are spoken in small areas of the community: the Leonese language, that “will be subject to specific protection […] because of its particular value within the Community’s linguistic heritage” and Galician language, which, according to the Statute of Autonomy, “will enjoy respect and protection in the places where it is usually used” (fundamentally, in the border areas with Galicia of the comarcas of El Bierzo and Sanabria). In the Salamancan comarca of El Rebollar, a modality of Extremaduran language is spoken (of the Asturian-Leonese branch) known as Palra d’El Rebollal. In Merindad de Sotoscueva (province of Burgos) a Castilian is spoken with some dialectal features of the Asturian-Leonese.