This publication elaborates upon the recommendations given in IAEA Nuclear Security Series No. 15, Nuclear Security Recommendations on Nuclear and Other Radioactive Material out of Regulatory Control, in relation to preventative measures. It serves as a guidance document for Member States interested in strengthening their nuclear security regime as it relates to nuclear and other radioactive material out of regulatory control and in improving their capabilities. The publication covers the following indicative elements: general considerations for preventive measures; deterrence measures; including deterrence by punishment and deterrence by denial, information security; promotion of nuclear security culture; measures for addressing the insider threat, including measures to promote the trustworthiness of personnel. The last section of the publication provides guidance for international cooperation and assistance to strengthen preventive measures.