This book examines how generative artificial intelligence is transforming the field of TESOL and second language education. It introduces the core principles of generative AI and explores its potential to reshape language teaching, learning, and assessment. Early chapters trace the historical development of TESOL theories and methodologies, showing how AI connects with evolving pedagogical approaches. Subsequent sections analyse current applications of AI-driven tools such as virtual tutors, language learning platforms, and automated assessment systems. Drawing on case studies and research, the book highlights best practices for educators and institutions seeking to integrate AI effectively and responsibly. Amongst other issues, key themes include ethics, privacy, bias, equity, and the future of teacher roles in AI-enhanced classrooms. Accessible and evidence-based, this book offers essential insights for educators, researchers, and policymakers interested in language education, AI integration, and applied linguistics.