Spanish is a Romance language with approximately 417 million speakers, 322 to 358 of whom speak it as a first language, while the remainder speak it as a second language. A significant number of people also speak Spanish as a foreign language. Spanish is spoken in Spain and is the official language of 20 other countries: Argentina, Bolivia, Chile, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, Equatorial Guinea, Guatemala, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Puerto Rico, Uruguay, and Venezuela. Spanish is also widely spoken in countries such as Andorra, Belize, the Philippines, and the United States.
Spanish first started to appear in writing in the form of notes and glosses in Latin religious texts, the Glosas Emilianenses, dating from the 11th century. During the 12th century, law codes (Fueros) were being translated into Spanish. Spanish prose flowered during the reign of King Alfonso X of Castile (1252-84), who in addition to being the king and a poet, also found time to write an encyclopedia in Spanish called Las Partidas, which contains laws, chronicles, recipes, and rules for hunting, chess, and card games. The first Spanish grammar, by Antonio de Nebrija, and the first dictionaries were published during the 15th and 16th centuries.
In Spain this language is generally called español (Spanish) when contrasting it with languages of other countries, such as French and English, but it is called castellano (Castilian, the language of the Castile region) when contrasting it with other languages spoken in Spain, such as Galician, Basque, and Catalan.
Beginning in the 1400s, Spanish explorers, conquistadors, and colonizers carried their language to Central America, South America, and parts of North America. The Spanish spoken in the Americas differs somewhat from European Spanish today because many words were borrowed from the languages of the indigenous peoples. Most of these words reflect features unique to the new territories, such as proper names, plants and animals, and geographic features. In 1565 Spanish conquerors and explorers established the settlement of Saint Augustine in what is now Florida. It was the first permanent European settlement in what is now the United States. In the 1600s and 1700s Spanish explorations and settlements extended the Spanish language north from Mexico into present-day Arizona, California, Southern Colorado, New Mexico, and Texas. When the United States annexed these areas following the Mexican War (1846-1848), many of the region’s Spanish-speaking inhabitants remained, creating a distinct linguistic and cultural population in the Southwestern United States.
Adapted from: http://www.omniglot.com/writing/spanish.htm and http://www.alsintl.com/resources/languages/Spanish/