As countries worldwide aim to reform their education systems and improve teaching and learning, lesson study (LS), which originated in East Asia, has recently attracted great attention. In order for international educators and policy makers to better understand the history and the state of the art of LS in East Asia, this article introduces three typical models in Japan, Mainland China and Hong Kong. First, they are described with regard to their distinct features, historical origin and development, goals and objectives, mechanisms of implementation, actual achievements, and structural constraints. Their commonalities and differences are then compared, and especially how and why these differences emerge in the specific sociocultural contexts of the regions. Finally, policy implications are discussed to provide insights for the other education systems in their policy making and implementation of similar reform practices.