Nuclear material accounting and control (NMAC) works in a complementary fashion with the international safeguards programme and physical protection systems to help prevent, deter or detect the unauthorized acquisition and use of nuclear materials. These three methodologies are employed by Member States to defend against external threats, internal threats and both State actors and non-State actors. This publication offers guidance for implementing NMAC measures for nuclear security at the nuclear facility level. It focuses on measures to mitigate the risk posed by insider threats and describes elements of a programme that can be implemented at a nuclear facility in coordination with the physical protection system for the purpose of deterring and detecting unauthorized removal of nuclear material.