At the end of the 19th century, the Parliamentary Republic took root by exalting the principles of 1789 French Revolution and rejecting personal power. Following this ideal, the Executive’s power to make regulations is dreaded – only allowed when strictly subordinate to the law supremacy. In the 20th century, the situation has changed. Wars and crises caused an essential transformation of the activities of the State, which disturbed the exercise of legislative functions and republican ideals. This thesis aims to explain how, between 1914 and 1958, the Executive Branch recovered a power to make regulations, that exceeds the mere implementation of legislation. The data show that this emancipation process stemmed from both disruption of practices and constitutional violations, gradually establishing a new law – thanks to the influence of law professors and advisory departments of the Conseil d’Etat. This dynamic relied on the need for Executive regulation to protect the security and the continuity of the State. Progressively, that kind of regulation got an autonomous constitutional basis, and the Executive enjoyed an increased level of discretion to enact it. The result is that, already under the Third and Fourth French Republics, the implementation of legislation no longer defined the source and the scope of the power to make regulations. Finally, these findings allow to challenge the current understanding of the Constitution of the Fifth Republic : the articles 16, 21, 34, 37, 38, 41 and 92 should no longer be considered as “innovations”, but only as a formalisation and a systematisation what previous constitutional law introduced.