Spanish (español), also called Castilian (castellano  listen (help·info)), is a Romance language that originated in Castile, a region in Spain. Approximately 406 million people speak Spanish as a native language, making it the second-most-spoken language by number of native speakers after Mandarin. It also has 60 million speakers as a second language, and 20 million students as a foreign language. Spanish is one of the six official languages of the United Nations, and is used as an official language by the European Union and Mercosur.

Spanish is a part of the Ibero-Romance group of languages that evolved from several dialects of common Latin in Iberia after the collapse of the Western Roman Empire in the fifth century. It was first documented in central-northern Iberia in the ninth century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia. From its beginnings, Spanish vocabulary was influenced by its contact with Basque and by other related Ibero-Romance languages and later absorbed many Arabic words during the Muslim presence in the Iberian Peninsula. It also adopted many words from non Iberian languages, particularly the Romance languages Occitan, French and Italian and increasingly from English in modern times, as well as adding its own new words. Spanish was taken to the colonies of the Spanish Empire in the sixteenth century, most notably to the Americas as well as territories in Africa, Oceania and the Philippines.