Spanish or Castilian (castellano) is a Romance language of the Indo-European language family that evolved from the Vulgar Latin spoken on the Iberian Peninsula of Europe. Today, it is a global language with about 500 million native speakers, mainly in the Americas and Spain, and about 600 million when including second language speakers. Spanish is the official language of 20 countries, as well as one of the six official languages of the United Nations. Spanish is the world's second-most spoken native language after Mandarin Chinese; the world's fourth-most spoken language overall after English, Mandarin Chinese, and Hindustani (Hindi-Urdu); and the world's most widely spoken Romance language. The country with the largest population of native speakers is Mexico.

The Indo-European languages are a language family native to the overwhelming majority of Europe, the Iranian plateau, and the northern Indian subcontinent. Some European languages of this family—English, French, Portuguese, Russian, Dutch, and Spanish—have expanded through colonialism in the modern period and are now spoken across several continents. The Indo-European family is divided into several branches or sub-families, of which there are eight groups with languages still alive today: Albanian, Armenian, Balto-Slavic, Celtic, Germanic, Hellenic, Indo-Iranian, and Italic; another nine subdivisions are now extinct.