European military transfusion services follow operational guidelines established by their respective national health systems and conform with European Union directives and NATO standards as applicable to member countries. Certain features are common to all of these standards, especially the pre-selection of volunteer, almost exclusively unpaid donors. NATO requirements are very close to European guidelines, with the exception that NATO permits the use of blood products collected in emergency conditions in theater when circumstances allow no better option. Blood product traceability exists for every country but is not always centralized or computerized. Serious adverse event reporting relies on national haemovigilance networks. Military considerations become important mainly in overseas operations, where the overall policy is to implement the relevant national, European or NATO guidelines with adjustments made for unique wartime circumstances and the risk/benefit ratio for the individual patient needing a transfusion.