“This outstanding anthology presents a multidimensional overview of approaches to action research. Drawing on research and practice in many different contexts the collection redefines the nature, scope and impact of action research and highlights the contribution it can make to teacher and institutional development and to student learning.”Jack C Richards, University of Sydney, Australia“This landmark handbook provides a thorough treatment of language teacher action research, showcasing its profound impact on teachers’ professional practice and development. Unparalleled in comprehensiveness, this volume is a seminal publication that advances our understanding of action research in language education. It provides an indispensable resource for practitioners, researchers, and teacher educators.”Icy Lee, National Institute of Education, Nanyang Technological University, Singapore“This Handbook marks an important milestone in our understanding of action research in the field of second-foreign language teaching. The 32 chapters detail a trajectory from early perceptions that often marginalized the work as ‘teachers fixing their teaching', to our present understanding of the methodology as part of a heuristic paradigm (Freeman & Cameratti 2019) which repositions teachers to generate unique knowledge about their work. The editors have done an excellent job of laying out the different spheres of impact of language teacher action research—professional, pedagogical, personal, and educational— in a volume that establishes its variety and breadth of productive benefits to the research, policy, and practitioner communities.”Donald Freeman, Marsal School of Education, University of Michigan, USA