An analysis of the risks and consequences of blue-on-blue (BoB) incidents is an important factor in the planning of the international operations of the Swedish forces. This report seeks to clarify some of the terminology and problems encountered when studying BoB-incidents. A selection of available data on BoB-incidents is presented, e.g. from the Kuwait war, along with a list of some of the aspects of the BoB-problem of greatest relevance to Swedish international operations. These include the demoralising effect on the troops, the consequences for cooperation with allied forces and the impact on support for international operations among the general public in Sweden.