This book introduces an approach to understanding and measuring working memory components and functions in second language learning, processing and development. It presents comprehensive, thorough and updated reviews of relevant literatures from cognitive sciences and applied linguistics. Drawing on multidisciplinary research, the book advocates a conceptual framework for integrating working memory theories with second language acquisition theories. An innovative theoretical model is also presented, which illuminates research studies investigating the distinctive roles of phonological and executive working memory as they relate to specific L2 learning domains, skills and processes. Theoretical and methodological implications of this integrative perspective are further elaborated and discussed within the specific realms of L2 task-based performance and language aptitude research.