The book explores principled methodologies for integrating artificial intelligence (AI) into language learning and teaching. It investigates the features of learner-AI interactions, second language (L2) acquisition theories and teaching methodologies, ChatGPT’s role in the development of the four language skills (listening, speaking, reading and writing), ChatGPT’s integration with form-focused, meaning-focused and content-based language learning, and individual differences in AI-facilitated learning. The book distinguishes itself by integrating theoretical evidence and practical applications, fostering an in-depth understanding of the application of AI in language education. By blending L2 acquisition theories and traditional pedagogy with the transformative capabilities of AI, this book offers a fresh perspective on language instruction. While the examples drawn on are from the teaching of Chinese and English as L2, the underlying principles, methodologies, and AI applications are relevant and can be directly applied to learning and teaching other languages.