For providing qualitative inclusion service to all students, general and special education teachers have competence to do the cooperative teaching(co-teaching). The purpose of this study was to explore the theoretical foundation of inclusion, co-teaching and implementing factors for effective inclusion. The conclusions were as follows. First, inclusion is the belief and philosophy that the education of students with disabilities are provided by not their disability but their ability. Second, out of inclusion models, co-teaching is the direct and substantial way to provide all students including students with disabilities. Third, the implementing factors of co-teaching are consisted of co-teaching relationship, co-teacher`s role, the model of co-teaching, the planning of co-teaching, curriculum adaptation and structure of general education classroom.