Language acquisition, the process by which children and adults learn a language or languages, is a major field of linguistic study.

A First-Language Acquisition  First-language acquisition is a complex process that linguists only partially understand. Young children have certain innate characteristics that predispose them to learn language. These characteristics include the structure of the vocal tract, which enables children to make the sounds used in language, and the ability to understand a number of general grammatical principles, such as the hierarchical nature of syntax. These characteristics, however, do not predispose children to learn only one particular language. Children acquire whatever language is spoken around them, even if their parents speak a different language. An interesting feature of early language acquisition is that children seem to rely more on semantics than on syntax when speaking. The point at which they shift to using syntax seems to be a crucial point at which human children surpass apes in linguistic ability.

B Second-Language Acquisition  Although second-language acquisition literally refers to learning a language after having acquired a first language, the term is frequently used to refer to the acquisition of a second language after a person has reached puberty. Whereas children experience little difficulty in acquiring more than one language, after puberty people generally must expend greater effort to learn a second language and they often achieve lower levels of competence in that language. People learn second languages more successfully when they become immersed in the cultures of the communities that speak those languages. People also learn second languages more successfully in cultures in which acquiring a second language is expected, as in most African countries, than they do in cultures in which second-language proficiency is considered unusual, as in most English-speaking countries.

C Bilingualism and Multilingualism  Bilingualism is the ability to master the use of two languages, and multilingualism is the ability to master the use of more than two languages. Although bilingualism is relatively rare among native speakers of English, in many parts of the world it is the standard rather than the exception. For example, more than half the population of Papua New Guinea is functionally competent in both an indigenous language and Tok Pisin. People in many parts of the country have mastered two or more indigenous languages. Bilingualism and multilingualism often involve different degrees of competence in the languages involved. A person may control one language better than another, or a person might have mastered the different languages better for different purposes, using one language for speaking, for example, and another for writing.