This paper discusses work done by the authors to develop an IAEA Nuclear Energy Series report to provide guidance on what would constitute an adequate justification process for a COTS device to be installed in a NPP for important to safety applications such that there is reasonable assurance of high quality and that the application of the COTS does not introduce new, unanalysed failure modes. The publication provides a process for justification of digital COTS devices that may be used to guide the incorporation of these devices into the design of I&C systems important to safety, such that there is sufficient evidence to demonstrate that these products have adequate integrity to meet the requirements for their intended nuclear applications.