This book provides a timely, comprehensive, and critically informed exploration of how Generative Artificial Intelligence (GenAI) transforms teaching practices, teacher preparation, and lifelong learning across diverse educational contexts. This book delves into how GenAI is used to enhance language teaching, improve assessment practices, foster inclusive pedagogies, and support teacher agency in navigating the ethical and practical complexities of the digital age. From personalized professional development frameworks to AI-powered instructional tools, this book addresses the opportunities and the challenges inherent in adopting GenAI in education. This book serves as a valuable resource for various audiences. For teacher educators, it provides a roadmap for incorporating GenAI into teacher preparation programs. For teachers, it provides them with tools to enhance pedagogical creativity and efficiency while maintaining critical engagement with AI. For policymakers and administrators, it presents evidence-based strategies for navigating the ethical and practical challenges of GenAI adoption. Most importantly, this book emphasizes the importance of empowering teachers as active agents in shaping the use of AI in education, ensuring that it aligns with human-centered and justice-oriented pedagogies.