Employing a mixed-method approach, the book investigates the psychology of English as a Foreign Language (EFL) teachers in the online teaching environment in China during the COVID-19 pandemic. Specifically, questionnaires were conducted on Chinese EFL teachers to explore the profiles of EFL teachers' anxiety, self-efficacy, buoyancy and engagement. Additionally, semi-structured interviews were used to demystify their psychological growth in the dynamic interaction with ecological environments, thus constructing an ecological model of EFL teacher psychology in online teaching. The book provides new insights into EFL teacher psychology and theoretical references for building a functional ecosystem for the professional development of EFL teachers. The book will be of interest to researchers in teacher psychology, language teachers and practitioners, especially those working in the complex technology-based educational environment, and policy makers in foreign language education.