This volume is dedicated to Bill Rutherford, a long-time friend and colleague, whosecommitment and dedication to the study of interlanguage has inspired many of us. The variouspapers deal with relevant issues in the study of interlanguage with the aim of addressing the widerange of theoretical and pedagogical questions that Rutherford has tried to answer throughout hiscareer. This multifaceted character of the book is very appealing, and so is the inquisitive andprovocative tone of several of the papers. I have chosen to group the contributions under fivedifferent headings, depending on the cognitive and behavioral sciences that constitute their mainfocus of attention.