This Element examines how generative artificial intelligence (GenAI) is reshaping educator professional development across initial teacher education, in-service learning, and institutional policy. It addresses two related but distinct topics: professional learning about GenAI, in which teachers develop the knowledge, skills, and judgement needed to use these tools responsibly, and professional learning through GenAI, in which GenAI serves as a vehicle for learning about topics such as assessment, differentiation, and pedagogy. It argues that GenAI's educational significance lies less in automating production than in intensifying the need for professional judgement. It introduces practical quality gates for evaluating AI-assisted materials, a functional typology of GenAI tools, design principles for GenAI-enhanced professional learning, and inquiry approaches, including a GenAI Learning Log, that centre teacher agency. Mini-scenarios and checklists illustrate low-risk, job-embedded ways to build critical AI literacy responsibly and with attention to equity.