Japanese Lesson Study has come under increasing attention from educators in the West and throughout South-East Asia since it was revealed outside Japan through the release of the TIMSS Video Study. In this paper we argue that Japanese Lesson Study provides a model for large scale, sustainable professional development. In particular, we draw on our own experience of Japanese Lesson Study and the research literature to describe its characteristic features and examine some of the cultural assumptions that underpin its implementation. (Contains 5 figures.)