This chapter discusses curriculum innovation and implication through Lesson Study as an effective model for improvement of school curriculum. Emphasis is placed on (1) the competency-based curriculum approach that focuses on students’ competencies, such as problem solving, communication and collaboration skills, and (2) the Integrated Studies period that had introduced in 1998 in Japanese national curriculum, and it has required teachers to develop school-based curriculum which has been involved local context and contents around the school. Lesson Study as school-based in-service development has empowered teachers to improve their ability to design new conceptualized school curriculum. From this chapter it can be seen that Lesson Study has been playing a role since the beginning of 2000s in the following three ways: (1) improving teachers’ pedagogical content knowledge, (2) promoting learning community and (3) expanding practical research in school and encouraging teachers as researchers. Lesson Study has been ‘discovered’ and ‘applied’ by these interrelated contexts of practical research. It focuses on ‘student learning’ rather than ‘teacher teaching’ and prefers ‘research in practice’ rather than ‘research on practice’.