This book describes the procedures, methods, measures and techniques which could be referred to as best practices when used by a State in establishing and maintaining the State System of Accounting for and Control of Nuclear Material (SSAC). Member States of the IAEA will use this publication as a guide in the accounting for nuclear material with the aim of improving the effectiveness of SSACs at the State and facility level, which is also an essential component in maintaining the security of nuclear material and combating illicit trafficking.