This book provides a comprehensive exploration of the transformative impact of generative AI in the field of TESOL. It addresses key topics that are highly relevant to educators, researchers, and policymakers working in the realm of second language education. The author first introduces the concept of generative AI, emphasizing its potential to reshape teaching and learning in TESOL, before delving into the historical development of TESOL, its evolving methodologies and theories. She explores how AI aligns with these theories, as well as examining research perspectives on AI's potential to revolutionize language education, and offers an in-depth analysis of the current state of AI in TESOL, illustrating the impact of AI-powered language learning apps, assessment tools, virtual tutors, and more. Supported by case studies, the book showcases best practices for educators to integrate AI into their teaching, addressing issues including privacy, bias, equity, autonomy, and job displacement, and highlighting the importance of responsible AI implementation.This book addresses the critical problem of adapting second language education to the transformative influence of AI, offering insights, solutions, and a forward-looking perspective for educators, researchers, and policymakers in the field of TESOL, as well as Applied Linguistics and Language Education more broadly.