This chapter discusses the evolution of different linguistic phenomena in Castile and León between the 13th and the 16th century. We study four historical corpora consisting of various original notarial and chancellor documents. For this purpose, we have accessed several corpora, representing three main distinct linguistic domains of Castile and León: the North of Burgos, shown in CODOMME; the South of Ávila, collected in CODOMSA and CODAHSA; and the West of León, compiled in CODOMSAE. The examined phenomena were the evolution of compound tenses, the devoicing of sibilants, and the evolution and aspiration of Latin F- (the latter is reflected in writing as , and ). These phenomena serve to illustrate the linguistic differences and similarities in different regions of Castile and León during the Middle Ages.