Spanish (also called Castillian to distinguish it from closely related languages like Catalan) is one of the Romance languages that evolved from Latin in the Iberian Penninsula. It is the official language of Spain and the the native language of most of the Spanish population although in some regions of Spain it is used together with one of the regional languages (Catalan, Galician and Basque are locally co-official with Spanish). Spanish is also the native language of Gibraltar, although the official language is English there.

Spanish was spread to territories outside Europe after the discovery of the Americas and the establishment of Spanish colonies there. Nowadays Spanish is the official language of Mexico and all countries of Central and South America, with the exception of Brasil, Belize, Guyana, Suriname and French Guiana. It is also the language of many islands in the Caribbean, and Spanish is also widely spoken in those states of the USA that formerly were part of Mexico. In Africa Spanish is the official language of Equatorial Guinea.

A characteristic of European Spanish (with the exception of the language spoken in southern Spain) as opposed to Latin American Spanish, is the pronunciation of Z and C (before E and I) as the TH in English think. In Latin America these letters are pronounced the same as the letter S, so Zorro is pronounced "Thorro" in Madrid but "Sorro" in Mexico City. Even with these differences in pronunciation (there are differences within Latin America as well) and the existence of words that are only used in some countries or regions (or words that have different meanings in different places) Spanish is a relatively homogeneous language.

The spelling of Spanish is fairly easy. When you see a Spanish word you can deduce from its spelling how it is pronounced. The reverse process is not always possible though. The letters B and V are for instance pronounced identically, but on the whole the Spanish orthography is very regular and consistent. Spanish uses the Latin alphabet like most European languages, but the letter K is used only in a handful of loanwords to represent the sound usually written as C or QU. The letter W is even rarer in Spanish than K. It is used in English loanwords like whisky.

Traditionally the digraphs CH, LL and RR were treated as separate letters of the Spanish alphabet and so was the letter Ñ. But nowadays words with these letters in them are usually ordered as they would be in English.

In syllables that are stressed irregularly an acute accent is used to indicate the vowel that should be stressed (e.g. mágico), and sometimes the acute accent is used with monosyllabic words to distinguish between homonyms, for instance si (if) and (yes). Another diacritical sign, the diaeresis, is used in a few words to indicate that in the groups GUE and GUI the U is not silent (contrary to the general rule). Most of these words are proper names like Güeldres (Guelderland) and Güimar.

Little is known about the language spoken in the Iberian Peninsula before the coming of the Romans. Some tribes spoke Celtic languages while others spoke languages that may or may not have been related to Basque. Of these pre-Roman languages only Basque has survived. All other Iberian languages spoken nowadays are descendants of Latin.

A noteworthy development during the evolution from Latin to Spanish is the replacement of the Latin f in front of a vowel by h (which has become a silent letter in Modern Spanish). There are Spanish words like factor where the f is used but all of these are loanwords. They are usually words that were borrowed from Latin in modern times (like factor) or borrowings from Classical Greek (e.g. físico). The loss of this f started in northern Spain and is perhaps due to Basque influence. In closely related languages like Portuguese and Catalan this change from f to h did not occur. Here are a few examples of words in which the f was replaced by h. This table also shows the corresponding Portuguese forms in which the f was retained:

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After the fall of the Roman Empire the Iberian Peninsula was invaded by Germanic tribes and one of the few Spanish words that were borrowed from their language was the word for goose, which is ganso (cf. German Gans). Much more influence on Spanish had Arabic which was brought to the peninsula by the Moors, an Islamic people from North Africa that invaded Iberia in 711 and conquered most of it. As a result of centuries of Moorish domination many words from Arabic, the language of Islam, are now used in Spanish. Many are easily recognizable because they start with al-, which is actually an Arabic article but was wrongly interpreted as a part of those words by the indigenous population (and probably by many of the Berber speaking Moorish conquerors as well). An example of an Arabic word in Spanish is almirante from amir-al-bahr ("prince of the sea"). This word also entered other European languages (English: admiral, French: amiral). Another example of Arabic influence is the word wadi (river) which is found in many Spanish river names, such as Guadalquivir and Guadalajara.

In the 11th century the Christians gradually began to reconquer the peninsula (La Reconquista) and push the Mohammedans southward, but only in 1492 did Granada, the last Islamic kingdom of Ibera, fall. Not many years thereafter a sailor from Genoa with the name of Cristoforo Colombo (Cristóbal Colón in Spanish, Christopher Columbus in English) discovered a few islands for the coast of what is now known as the Americas, and as a result of this discovery one of the largest empires in history came into being. This empire once covered vast areas of North and South America, and there were also Spanish colonies in Africa and in the Pacific (e.g. the Philippines). Nowadays the Canary Islands and two small enclaves on the Moroccon coast are the only remnants of the Spanish Empire outside Europe, but the language of this empire is spoken by millions in many other countries.

As an important world language Spanish has naturally attributed words to many other languages. Papiamento in the Caribbean is a creole language that is mainly based on Spanish and Portuguese, Chamorro on the island of Guam is an Indonesian language with a large number of Spanish words in its vocabulary, and the same is true for Tagalog, the most widely spoken indigenous language of the Philippines.

English too has borrowed its share of Spanish words, like junta, rodeo, cañon, guerilla, ranch, siesta and torero. Many of these words came into English in the New World and there are even five states in the USA that have Spanish names: Arizona (arid zone), Colorado (reddish), Florida (flowery), Montana (mountain) and Nevada (snow-covered). And even those who have never learnt a single word of Spanish will recognize the names of the American cities Los Angeles and El Paso as being originally Spanish names.