The advent of the latest artificial intelligence (AI) technology, such as large language models (LLM), and AI services, such as ChatGPT, has the potential to reform the way we learn a language and the way we study language learning. The widespread interest in ChatGPT shows text writing, rephrasing, correction, and even translation have become easily accessible to people from all walks of life. With its capacity to simulate complex human-like interactions and offer immediate, nuanced feedback, AI serves as a potent tool for enhancing the effectiveness of language acquisition. Given these opportunities and demonstrated efficacy, AI-mediated language learning (AIM-LL) will be an active research area for a long time to come. This chapter provides an overview of the technology behind ChatGPT to enable a more comprehensive engagement with this AI system. We also include case studies on language learning using ChatGPT and other AI tools to showcase opportunities in AI-mediated language learning and research. Yet, as promising as these prospects are, they do not come without challenges. These include ethical concerns, the digital divide, and the potential loss of the human touch in language education. This chapter specifies some of these challenges, offering a balanced perspective on the role of AI in language learning. Finally, we point out future technological innovations following the success of ChatGPT to provide insight into the trajectory of AI development. This topic is relevant to language learners, educators, researchers, technologists, and policymakers interested in the future of language education.