This book examines different theoretical perspectives on the role that interaction plays in second language acquisition. The principle perspectives are those provided by the Interaction Hypothesis, Socio-Cultural Theory, and the Levels of Processing Model. Interaction is defined broadly; it is seen as involving both intermental and intramental activity. The theoretical perspectives are explored empirically in a series of studies that investigate the relationship between aspects of interaction and second language acquisition. A number of these studies consider the effects of interaction on the acquisition of vocabulary (word meanings) by both adult and child second language (L2) learners. In addition, the effects of language aptitude on input processing are considered, as well as the contribution that interaction makes to the acquisition of grammatical knowledge. These studies provide clear evidence that social and intermental interaction are major forces in the acquisition of an L2. Finally, the book considers a number of pedagogic specifications, in particular the importance of discourse control as a means of learners' obtaining the quality of interaction likely to foster L2 acquisition. The book is divided into 11 chapters spread across 2 sections. References and an index are included. (Author/KFT)