This chapter examines contemporary uses of generative artificial intelligence (GenAI) in TESOL, drawing on emerging scholarship and empirical evidence from an international mixed-methods study. It analyses educators’ reported applications of GenAI for writing support, conversational practice, content generation, real-time feedback, and teacher-facing tasks such as lesson planning and assessment design. Findings indicate that many teachers value GenAI for enhancing efficiency, personalisation, and learner engagement, including low-anxiety opportunities for interaction and adaptive support. However, participants also highlight persistent risks, notably over-reliance, weakened critical thinking, plagiarism and assessment challenges, and students’ uncritical trust in AI-generated outputs. Adoption trends are interpreted through a multi-theoretical lens: social constructivism foregrounds scaffolding and learner autonomy; the Ethical Use of Technology framework emphasises privacy, bias, accountability, and misinformation; critical theory highlights inequitable access and cultural relevance; and the Technology Acceptance Model (TAM) explains uptake in relation to perceived usefulness, ease of use, and external constraints. The chapter concludes that GenAI’s pedagogical value depends on explicit guidance, professional development, and institutional policies that support equitable, ethical, and critically mediated classroom integration.