Each State has the primary responsibility to build the capacity of organizations and people in order to develop, implement, and sustain a nuclear security regime. To discharge its responsibilities, the State has to strengthen its capacity at national, organisational and individual levels. Specifically, the State has to be able to enhance the competences and capabilities of relevant stakeholders in fulfilling their responsibilities within the nuclear security regime. Such endeavour involves various elements in capacity building, ranging from education and training to the development of knowledge network. This publication is intended to serve as a reference document for Member States to develop a national capacity building strategy for nuclear security. It addresses all organizations involved in nuclear security and reflects the multidisciplinary and cross-institutional nature of this task, as well as the long term efforts that are required.