This subject of this book is the lexicon in second language acquisition (SLA). The most simple definition of lexicon is the list of words in a language, or the vocabulary. One might imagine, then, that learning the vocabulary of a second language (L2) may just mean learning which words mean'the same'as ones in the first language. However, there is much more to learning words than one-to-one matching of L2 words to native language equivalents. The claim will be that in second language acquisition, as well in first language acquisi tion, the learner brings a considerable amount of internal knowledge to bear on the problem of learning words and their meanings, and that without this internal contribution, much of the knowledge which speakers of second languages possess could not be explained. As a result of this perspective, much of the book will be devoted to an analysis of theories of the linguistic system which underlies the knowledge learners bring to the problem of learning properties of words.

Gass & Schachter (1989, p. 201) noted that, in spite of the importance of the lexicon in SLA, surprisingly little research had been devoted to this topic. This situation has changed somewhat in the past five years, but most often research carried out by applied linguists treats the lexicon as synonymous with'vocabulary'learning; in this way, the lexicon is often understood to mean'word list'. Hence, research has focused on word lists, L2 acquirers' knowledge of and ability to remember words, and, occasionally, issues related to the traditional notion of collocation, and transfer of cognates (see for