Spanish (español ) or Castilian (castellano) is a Romance language originally from the northern area of Spain. From there, its use gradually spread inside the Kingdom of Castile, where it evolved and eventually became the principal language of the government and trade. It was later taken to Africa, the Americas and Asia Pacific when they were brought under Spanish colonial rule between the 15th and 19th centuries. Today, it is one of the official languages of Spain, most Latin American countries and Equatorial Guinea. In total, 21 nations use Spanish as their primary language. Spanish is also one of six official languages of the United Nations. The language is spoken by between 322 and 400 million people natively, making Spanish the most spoken Romance language and possibly the second most spoken language by number of native speakers. Mexico has the world's largest Spanish-speaking population. Spanish is the second most widely spoken language in the United States and by far the most popular studied foreign language in U.S. schools and universities. Spanish is among the most popular foreign languages for study in the rest of the nations of the Anglosphere in general, where on top of the widespread use of English globally, the large number of additional countries and geographic territory that Spanish allows exploring is an attractive prospect for many people. Due to proximity, linguistic similarities, and trade reasons it is also a very popular second language in France, Italy, Portugal, and particularly the southern states of Brazil. It is estimated that the combined total of native and non-native Spanish speakers is approximately 500 million, likely making it the fourth most spoken language by total number of speakers. Global internet usage statistics for 2007 show Spanish as the third most commonly used language on the internet, after English and Chinese. Spaniards tend to call this language español (Spanish) when contrasting it with languages of other states, such as French and English, but call it castellano (Castilian), that is, the language of the Castile region, when contrasting it with other languages spoken in Spain such as Galician, Basque, and Catalan. This reasoning also holds true for the language's preferred name in some Hispanic American countries. In this manner, the Spanish Constitution of 1978 uses the term castellano to define the official language of the whole Spanish State

Psycholinguistics is the psychology of language and the study of the psychological and neurobiological factors that enable humans to acquire, use, and understand language. Psycholingusitics research makes use of biology, neuroscience, cognitive science, and information theory to study how the brain processes language. There are a number of subdisciplines; for example, as non-invasive techniques for studying the neurological workings of the brain become more and more widespread, neurolinguistics has become a field in its own right.The study of word recognition and reading examines the processes involved in the extraction of orthographic, morphological, phonological, and semantic information from patterns in printed text. Psycholinguistics covers the cognitive processes that make it possible to generate a grammatical and meaningful sentence out of vocabulary and grammatical structures, as well as the processes that make it possible to understand utterances, words, text, etc. Developmental psycholinguistics studies children's ability to learn language.