Kyouzai kenkyuu, or the “study of materials for teaching”, is a critical yet often neglected phase in lesson study adopted in countries beyond Japan. In this phase, teachers carefully examine curriculum documents, textbooks, teaching and learning materials, and subject matter and read relevant research to inform the development of a unit within which is embedded the research lesson. However, teachers often fail to engage adequately in kyouzai kenkyuu. Given its importance, it is crucial for teachers to understand the essence of kyouzai kenkyuu and conduct this phase of lesson study beyond a superficial level. In this chapter, we will explain the main inquiry processes involved in kyouzai kenkyuu, provide some guidelines for lesson study practitioners, and illustrate these ideas using two snapshots of practice from our work with teachers.