This singular new textbook is both an introduction to the major theories of second language acquisition and a practical proposal for their application to language learning courses. It explains and evaluates these theories, and focuses on recent research that has enriched thinking about the best ways to facilitate communicative effectiveness in an L2. It then suggests practical applications regarding language planning, curriculum development, pedagogy, materials development, teacher development, and assessment, establishing a tangible connection between theory and practice. Unlike many SLA books which are narrowly focused on the acquisition of language, it explores the roles of factors such as pragmatics, para-linguistic signals, gesture, semiotics, multi-modality, embodied language, and brain activity in L2 communication. SLA Applied connects research-based theories to the authors' and students' real-life experiences in the classroom, and stimulates reflection and creativity through the inclusion of Readers' Tasks in every chapter. This engaging and relevant text is suitable for students in Applied Linguistics or TESOL courses, trainee teachers, researchers, and practitioners.