The significance of cross-linguistic influences has long been a controversial topic. As this book indicates, the controversy has had a long life not only among second language teachers and researchers, but also among linguists interested in questions of language contact and language change. Although it would be too much to hope that this book will cause such a long-standing controversy to die, the discussion of transfer here may help to set to rest some dubious claims and to point the way toward more productive thinking about cross-linguistic influences. While I have tried hard to avoid the sweeping claims that unfortunately have been frequent in discussions of transfer, I make no secret of my belief that transfer is an extremely important factor in second language acquisition. The available evidence, I feel, warrants that belief. Thus, the focus of this book is on empirical investigations of learners' behavior in many contexts. There is some discussion of the pedagogical implications of certain investigations, but it seems to me that relatively little is known about the best ways to make use of transfer research in the classroom – hopefully, more teachers and teacher trainers will begin to think about what those ways are. There is also some discussion of theoretical work in other areas of linguistics, but I have made efforts to limit that discussion, which could go on interminably, and to limit the jargon that usually accompanies such discussion.