This publication presents a systematic approach to establishing and operating a national nuclear security support centre (NSSC) as a means to strengthen the sustainability of nuclear security in a State. It provides specific practical guidance to States, detailing a straightforward decision making and project management process drawn from good practices in establishing and operating an NSSC that were identified through the experience and lessons learned from States within the NSSC Network. The publication, which is a revision of TECDOC-1734, is intended for use by the IAEA and the NSSC Network as the primary reference for activities to support States with the establishment and operation of an NSSC.