With the increasing importance of teaching sustainable development (SD) in cultivating knowledgeable and responsible citizens who actively contribute to the environment, economy, and society, there is a pressing need for expertise within the teaching profession, particularly among social studies educators. This research aims to explore the professional knowledge, skills, and wisdom of social studies teachers in effectively integrating SD into the current geography curriculum. Seven high school geography teachers participated in this multiple case study, revealing the distinct knowledge base components necessary for teaching SD in the geography classrooms. Findings reveals how geography teachers utilize and evolve their professional knowledge base and the interplay between these components through the transformations in teachers’ knowledge bases before, during, and after professional development.