This publication provides guidance to States, competent authorities and operators on appropriate nuclear security measures during each stage in the lifetime of a nuclear facility, from initial planning of the facility through to its final decommissioning. The publication addresses effective nuclear security in the transition between stages and applies to the nuclear security of nuclear material and nuclear facilities throughout the lifetime of all types of nuclear facility. Although focused on nuclear power, the guidance contained in this publication may be useful for States developing nuclear programmes with other types of facility, including those for research and development.