Where the study of linguistics concerns itself with solving practical problems, applied linguistics is the result. This field may use insights from theoretical linguistics in approach issues within second language acquisition or language education in particular, but some see it as including any application of theoretical language study, incorporating other fields such as clinical linguistics and language planning. In addition, applied linguistics itself has seen its own theories emerge over the years.
In the USA, the American Association for Applied Linguistics started convening conferences in the 1970s. The UK equivalent is the British Association for Applied Linguistics; the Association Internationale de Linguistique Appliquée is an international group. Research appears in several journals.
Language Education and Teaching
Virtually every applied linguistics university degree programme in the world stresses and at the very least includes research and practice in language education and teaching of languages—usually second languages or foreign languages but not infrequently, first languages. The two terms here, education and teaching, may often be used interchangeably. However, if one were to enquire of university faculty (and other organisations) that prepare teachers to teach and do research in education what the difference would be, education would embody the goals and rationale of learning and how it could be accomplished and verified, while teaching would embody the methods and practices of how one person educates or trains another person. Education can be a solitary pursuit or it may involve a guide, the teacher, who directs, instructs and mentors the student formally in a classroom or in other settings. But even the role of the teacher would embody a social and political philosophy and what and how something is learned could cover a broad spectrum from open-minded education to politically focused indoctrination. This then would be a very simplified working definition of these two terms that could be gathered from multiple sources: Education is, generally speaking, the process of learning while teaching is the act of overseeing the process of learning. 
Research in language teaching
Today, 'applied linguistics' is sometimes used to refer to 'second language acquisition', but these are distinct fields, in that SLA involves more theoretical study of the system of language, whereas applied linguistics concerns itself more with teaching and learning. In their approach to the study of learning, applied linguists have increasingly devised their own theories and methodologies, such as the shift towards studying the learner rather than the system of language itself, in contrast to the emphasis within SLA.
The field of applied linguistics first concerned itself with second language acquisition, in particular errors and contrastive analysis, in the 1950s and 1960s. In the 1970s, with the failure of contrastive analysis as a theory to predict errors, second language researchers began to adopt Noam Chomsky's theory of universal grammar to explain second language learning phenomena; its impact in applied linguistics and language teaching was more limited. In the 1990s, more and more researchers began to employ research methods from cognitive psychology. Researchers are mainly drawn from linguistics, anthropology, psychology, and education.
Clinical linguistics entails the application of linguistics to speech-language pathology. This involves treating individuals whose linguistic development is atypical or impaired. This branch of applied linguistics may also involve treatment of specific language impairment, where one aspect of language develops exceptionally. The field has also adopted existing ideas which have have not become 'mainstream' in theoretical linguistics. For example, both behaviourism and natural phonology have appeared in the literature.
Computerised text analysis
Textual analysis performed by computer can be implemented using a number of open source software tools. The Python programming language supports regular expression processing. Regular expressions for characters are the linguistic equivalent of algebraic expressions for numbers in mathematics. Additional open-source software tools that can be used for parsing and generating passages of written text include sed, awk, lex, yacc, perl, and ruby.
- Teaching Princeton University WordNetWeb; Teacher Teaching Terminology of Technical and Vocational Education - Revised Edition 1984. New Zealand Digital Library, University of Waikato; Definitions Justia US Laws, Supreme Court Center, Title 7 Agricutlure, Institution capacity building grants program, 7 C.F.R. § 3406.2 Definitions.; Good Teaching-Top ten requirements Richard Leblanc, York University, Ontario (1998); Teaching Tips Index Honolulu Community College Faculty Development; Teaching Tolerance Southern Poverty Law Center; Teaching Jere Brophy, Int'l Academy, of Education, Int'l Bureau. of Education, UNESCO
- The applied linguist Vivian Cook has, for example, introduced the term L2 user as distinct from L2 learner (see Cook's page: Background to the L2 User Perspective). The former are active users of the language; the latter those who learn for later use. Cook's view also severs a link to SLA, in that a user's language ability is seen not as an approximation towards native speakers' competence, but as a system in its own right.
- See also Wei (2007) for an appeal to focus on the learner rather than the system. Wei L (2007) 'A user-friendly linguistics.' International Journal of Applied Linguistics 17: 117.
- e.g. Chomsky (1957).
- Hymes (1972) outlined a theory of education in opposition to what some applied linguists and educators perceived to be inadequacies in Chomsky's ideas of linguist competence for developing teaching methodologies. However, Chomsky and his associates never presented 'universal grammar' as relevant to language teaching.
- The most famous case is Genie, an individual who was deprived of language throughout much of her childhood.
- Bishop (2006).
- Castagnaro (2006), for review.
- Grunwell (1997).