Spanish or Castilian (castellano) is a Romance language that originated in northern Spain, and gradually spread in the Kingdom of Castile and evolved into the principal language of government and trade. It was taken to Africa, the Americas, and Asia Pacific when the Spanish Empire was established between the 15th and 19th centuries. Today, between 322 and 400 million people natively speak Spanish, making it the world's second most-spoken language by native speakers (after Mandarin Chinese).

It is estimated that the combined total of native and non-native Spanish speakers is approximately 500 million, likely making it the third most spoken language by total number of speakers (after English and Chinese).

Today, Spanish is an official language of Spain, most Latin American countries, and Equatorial Guinea; 21 nations speak it as their primary language. Spanish also is one of six official languages of the United Nations. Mexico has the world's largest Spanish-speaking population, and Spanish is the second most-widely spoken language in the United States and the most popular studied foreign language in U.S. schools and universities. Global internet usage statistics for 2007 show Spanish as the third most commonly used language on the internet, after English and Chinese.Spanish has been described as the third most influential language in the world (after English and French).