Abstract: Can constitutions successfully constrain the exercise of the treaty power? This article examines the French Constitution of 1958 as a case study. The founders of the Fifth Republic drafted provisions intended to protect national sovereignty, as the Gaullists understood that concept, against inroads resulting from international agreements. Looking back fifty years later, it is clear that those protective efforts did not succeed. The sequence of events by which the constraints were loosened or evaded may represent one nation's particular history, but they illustrate the limited capacity of constitutional restrictions to control international commitments in the long term.