This volume examines the agency of second/foreign language teachers in diverse geographical contexts and in both K-12 and adult education. It offers new understandings and conceptualizations of second/foreign language teacher agency through a variety of types of empirical data. It also demonstrates the use of different methodologies or analytic tools to study the multidimensional, dynamic and complex nature of second/foreign language teacher agency. The chapters draw on a range of theories and approaches to language teacher agency (including ecological theory, positioning theory, complexity theory and actor-network theory) that expand our understanding of the concept, while at the same time presenting various analytic approaches such as discourse studies and narrative inquiry. The chapters also analyze the connection of agency to other relevant topics, such as teacher identity, emotions, positioning and autonomy. This book contains the following chapters: (1) Introduction (Hayriye Kayi-Aydar, Xuesong Gao, Elizabeth R. Miller, Manka Varghese, and Gergana Vitanova); (2) Language Teacher Agency: Major Theoretical Considerations, Conceptualizations and Methodological Choices (Hayriye Kayi-Aydar); (3) Examining High School English Language Learner Teacher Agency: Opportunities and Constraints (Aliza Fones); (4) 'What If You Don't Have Boots', Let Alone Bootstraps? An ELL Teacher's Use of Narrative to Achieve and Generate Agency in the Face of Contextual Constraints (G. Sue Kasun, J. Spencer Clark, A. Jyoti Kaneria, and Emmie Staker); (5) Language Teacher Agency and High-Stakes Teacher Evaluation: A Positioning Analysis (Amber N. Warren); (6) Using Actor-Network Theory to Problematize Agency and Identity Formation of Filipino Teachers in Japan (Alison Stewart); (7) World Language Teachers Performing and Positioning Agency in Classroom Target Language Use (Michele Back); (8) Bi/Multilingual Teachers' Professional Holistic Lives: Agency to Enact Inquiry-Based and Equity-Oriented Identities across School Contexts (Patricia Venegas-Weber); (9) English Language Teachers' Agency and Identity Mediation through Action Research: A Vygotskian Sociocultural Analysis (Emily Edwards); (10) Problematizing English Language Teaching in China through a Local Chinese English Teacher Agency Lens (Wenjing Li and Peter De Costa); (11) Teacher Authority and the Collaborative Construction of Agency in Second Language Writing Instruction (Patricia Mayes); (12) Language Teacher Agency: A Critical Realist Perspective (Karin Zotzmann); (13) Volunteer Teacher Agency in a Church-Based ESL Program: An Ethnography (Xia Chao); and (14) English Language Instructors, Medium of Education and Professional Agency: An Indian Perspective (Priti Sandhu). [Afterword by Anne Feryok.]