This publication provides detailed guidance on developing, implementing, and integrating computer security as a key component of nuclear security. This guidance applies to computer security aspects of nuclear security and its interfaces with nuclear safety and with other elements of a State's nuclear security regime, including the security of nuclear material and nuclear facilities, of radioactive material and associated facilities, and of nuclear and other radioactive material outside of regulatory control. The scope of this publication includes: computer-based systems, the compromise of which could adversely affect nuclear security or nuclear safety; the State's and relevant entities roles and responsibilities in relation to computer security in the nuclear security regime; the activities of the State in establishing and implementing a computer security strategy for nuclear security; the elements and measures for subordinate computer security programmes; and the activities to sustain the strategy.