The aim of this study is to explore the pedagogical reasoning and action of high school geography teachers when teaching sustainable development within the context of the Advanced Placement Human Geography classroom. Through a multiple case study approach, this research examines the instructional decisions and rationales of seven APHG teachers throughout their entire teaching activities. The findings illuminate how participating teachers make informed instructional decisions through specific teaching strategies and practices and the rationale behind their decisions, encompassing both planned pedagogical actions and responses to unexpected instructional challenges in their classrooms.