This textbook presents an up-to-date account of the main concerns, problems and theoretical and practical issues raised by second language acquisition research. Research in this field has until recently been mainly pedagogically, oriented, but since the 1970s linguists and psychologist have become increasingly interested in the principles that underlie second language acquisition for the light these throw on how human language processing functions in general. Moreover, it is only through an understanding of these principles that foreign language teaching can become maximally effective.