In search of realization of the principle of legality in the armed forces the paper deals with the translation of the German concept “Citizens in Uniform”. Furthermore, the paper also suggests principle answers about the relation between legality and opportunity in the organization and functioning of the armed forces and it formulates the criteria of legality. The application of these criteria can serve for the evaluation of the domain of the rule of law in concrete armed forces, and comparative legal comparison with others. The criteria can be used as a test for legality of legal acts which regulate military organization. Those who practice law and those who are connected with armed forces can use it for the interpretation and application of law.