This book explores principled approaches to integrating Generative Artificial Intelligence (GenAI) into language learning and teaching. It examines the features of learner-AI interaction, the affordances of GenAI, and key principles that guide its use in language education. Drawing on second language acquisition theories and teaching methodologies, the book investigates how GenAI can support the development of listening, speaking, reading, and writing, as well as task-based language teaching. Illustrated through concrete prompting activities, Using Artificial Intelligence in Language Education translates theory and research into practical pedagogy for meaningful AI-mediated language learning. It empowers teachers to use GenAI confidently and to help learners engage in purposeful learning experiences. Filling a critical gap by offering language learners and teachers principled guidance and practical examples, this is also an indispensable source of ideas for learners and teachers to develop their own applications.