This article analyses the requirement of parliamentary approval for the deployment of armed forces under the provisions of the Basic Law that concern defence. It discusses continuity and change in its constitutional foundations and its doctrinal shape in light of the Federal Constitutional Court's recent Libya judgment of September 2015 and the reform proposals for the Parliamentary Participation Act of 18 March 2005. Reading the case law comprehensively, one can see that the requirement of parliamentary approval fulfils a 'double compensatory function'. At the outset, in the AWACS/Somalia judgment of 1994, the Federal Constitutional Court developed the requirement of parliamentary approval for the deployment of armed forces in order to keep the balance between relevant executive and legislative powers. It was intended to compensate for the broad executive powers in the progressive development of international treaties. In part, this function has been accomplished by the ensuing parliamentary practice at least for the time being. Today, the requirement of parliamentary approval essentially fulfils a 'compensatory' function of a different kind: The requirement to involve the parliament particularly compensates for the broad powers to deploy armed forces within systems of collective security. Substantially, the decision on deploying armed forces is rather underdetermined and this situation creates the need for a more demanding procedure and the involvement of parliament. Beyond its constitutional foundations, the evolution of the requirement of parliamentary approval also affects its doctrinal shape. Originally, the requirement of parliamentary approval for the deployment of armed forces was accorded a doctrinal special status. This special status can be explained by its unique function in coping with the epochal change of 1990. In later case law, and on the basis of parliamentary practice, this special status has been attenuated. The Federal Constitutional Court has gradually integrated the requirement of parliamentary approval for the deployment of armed forces into the general constitutional doctrines of the rule of law and democracy, balance of powers and the theory of 'legislative reservation' (Wesentlichkeitstheorie). This development is not only of theoretical interest, but is relevant for the question of which situation constitutes an 'involvement in armed operation' and triggers the application of the constitutive requirement of parliamentary approval. On the one hand, the Libya judgment, at least in part, questions the significance of the requirement of parliamentary approval for the rule of law and democracy. On the other hand, the judgment also values the role of the parliament and follows the general trend of including the requirement of parliamentary approval for the deployment of armed forces into the theory of 'legislative reservation' and the general constitutional balance of power doctrine.