This book reconsiders a question that many language teachers and educational researchers have addressed: How much influence can a learner's native language have in making the acquisition of a new language easy or difficult? Transfer has long been a controversial issue, but many recent studies support the view that cross-linguistic influences can impact second-language acquisition. The author analyzes and interprets research showing many ways in which similarities and differences between languages can influence the acquisition of grammar, vocabulary, and pronunciation. In addition, he provides a detailed look at work in other areas important for the study of transfer, including discourse, individual variation, and sociolinguistics. Language teachers, applied linguists, and educational researchers will find this volume highly accessible and extremely valuable to their work.