There is a sense in which almost any statement about language, language learning or language teaching may be said to hold implications for a view about language learning or teaching expertise. Thus an observation about the nature of language implies a view about what it is that an expert user of the language is able to do. Similarly, a statement about language learning is interpretable as an observation about the processes which an expert learner has successfully undertaken.By now, at the start of the twenty-first century, expertise studies have been undertaken in a large number of domains (and Table 1.1 of Chapter 1 lists a number of them). Applied linguistics is a relative newcomer to the list, and this is in itself a major reason why the time is ripe for a volume looking at what has been done in other domains, as well as what is emerging in the areas of second language learning and teaching.
