The second edition of Theories in Second Language Acquisition seeks to build on the strengths of the first edition by surveying the major theories currently used in second language acquisition research. This volume is an ideal introductory text for undergraduate and graduate students in SLA and language teaching. Each chapter focuses on a single theory, written by a leading scholar in the field in an easy-to-follow style - a basic foundational description of the theory, relevant data or research models used with this theory, common misunderstandings, and a sample study from the field to show the theory in practice. This text is designed to provide a consistent and coherent presentation for those new to the field who seek basic understanding of theories that underlie contemporary SLA research. Researchers will also find the book useful as a quick guide to theoretical work outside their respective domains.