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 psychologists 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. In the first part of his book, Wolfgang Klein provides a critical assessment of the current state of the art. The second part, 'from the learner's point of view', is devoted to four central problems which anyone learning a second language (either through everyday communication or in the classroom) is faced with, and whose solution constitutes the acquisition process. This accessible introduction provides students of linguistics and applied linguistics and anyone concerned with foreign language teaching with a real understanding of the fundamental issues in the field, or the advances that have not yet been solved and sometimes not even approached.