This book represents a personal survey and interpretation of the role of working memory (WM) in first and second language acquisition (SLA). Through this book, I hope to bring together and integrate major areas of my current research interests, namely WM research in cognitive science and SLA research in applied linguistics.

Before I embarked on this project 10 years ago, I intended to write an updated and extended version of Susan Gathercole and Alan Baddeley's seminal book Working Memory and Language (1993). Greatly motivated by their pioneering work, I have always held the view that WM should play a greater role in second language learning than in first language acquisition, and that the very topic of working memory and second language learning should deserve an independent book-length volume in its own right. My long-held conviction on this WM–SLA enterprise was greatly reinforced by Professor Alan Baddeley's opening speech (titled 'Working memory at 40') delivered at the 2014 International Conference of Working Memory held at Cambridge University, which marked the 40th anniversary of the seminal multi-component model of WM (i.e. Baddeley & Hitch, 1974). Most encouraging and relevant of all, Baddeley concluded his speech by predicting that 'WM and second language learning' would be one of the more promising areas of WM research in the next decade. I am very pleased and grateful indeed to Professor Baddeley for sharing his insights and vision for the WM–SLA enterprise with me during my short stint at Cambridge. Of course, I am even more grateful to Alan for contributing the introductory chapter to my recent co-edited volume (Wen et al., 2015) on this same topic (Baddeley, 2015), and for his endorsement written for this current volume as well (as printed on the back cover). Above all, I wish to thank Professor Baddeley for introducing the classical WM model, which has inspired most of the WM–SLA explorations in applied linguistics and also laid the theoretical foundation for the integrated perspective on WM and SLA that I propose in this book.