Spanish, along with French, Italian, Catalan, Portuguese, and Romanian, is a Romance language—that is, it derives from Latin, the language of the Romans. The history of the Spanish language can be said to have begun with the linguistic evolution of Vulgar or spoken Latin, a Latin that was formed when the classical Latin of the conquerors mixed with the pre-Roman languages of the Iberians, Celts, and Carthaginians.

Before the Roman conquest of 19 B.C., Spain was occupied by the native Iberians, the nomadic Celts and the conquering Carthaginians. The languages of these people sometimes mingled together and often remained distinct. Under Roman rule, the inhabitants, for practical purposes, were compelled to learn Latin, and in their daily life they often mixed Latin with their native tongues. This mixed or Vulgar Latin became the predominant and official language of the region, and remained so even during the Visigothic invasion in the beginning of the fifth century.

Things changed only with the Moorish invasion in the eighth century, when Arabic-speaking Moors from Northern Africa completed their conquest of the region. The Moors maintained their language, religion, and culture by speaking Arabic and a related dialect called Mozarabic, and, consequently, exercised a significant effect on the history of the Spanish language. The influence is only lexical and not grammatical, but Arabic loan-words exist in Spanish in the thousands. The great majority of these are nouns, such as alcalde (mayor), almirante (admiral), alquiler (rent), acequia (ditch), alfarero (potter). Place names of Arabic origin are also common (Madrid, Guadalquivir). Vulgar Latin survived only in a few remote Christian kingdoms in the North such as Asturias.

From the eleventh century onwards, the northern Christian kingdoms gradually reconquered Moorish Spain, imposing their language and culture as well as their politics on the country. As the Castilians of the Northern Central Plains were particularly successful, their dialect, called Castilian, established itself as the language of power and prestige. The creation of a standardized Spanish language based on the Castilian dialect began in the thirteenth century with King Alfonso X, who was called the Learned King of Castile and Leon. His scholars wrote original works in Castilian and translated histories, chronicles, and scientific, legal, and literary works from other languages (principally Latin, Greek, and Arabic).

Alfonso X adopted Castilian for all official work. His successors, Isabella and Ferdinand, made Castilian the official language in their kingdom. An important book ‘Arte de la lengua castellana’ (The Art of the Castilian Language) appeared during the reign of the Catholic Kings which was a work of Antonio de Nebrija. It was the first book to study and attempt to define the grammar of any European language. The Castilian dialect became the medium for writing and education in Spain, even though several spoken dialects remained in use. The most noteworthy was Andalusian, a dialect spoken in the southern city of Seville in the Andalusia region.