Most second language acquisition research has been concerned with grammar or phonology and has failed to discuss lexical acquisition. The main reason for this neglect has been the lack of vocabulary study by linguists. However, recent concern with semantic theory has brought new impetus to work on lexical acquisition. Useful research on lexical acquisition is dependent upon a number of fundamental theoretical issues. Among these are: (1) whether the processes whereby second language vocabulary is acquired parallel those by which first language vocabulary is acquired, (2) what individual personality characteristics affect the learning and use of vocabulary, (3) the stages by which the lexical stock of a second language learner grow and expand and the factors which influence this growth and expansion, (4) the relationship between active/productive and passive/receptive knowledge of vocabulary, and (5) the kinds of research in lexical acquisition further required. Factors that affect the growth and expansion of second language vocabulary include phonological, morphological, syntactic, and semantic features of the learner's first language, second language, and other Languages with which s/he is acquainted. In addition, the personality, motivation, and knowledge of the learner and the situation in which the learning takes place affect lexical acquisition. (JK)