Increased cohesion of groups and political blocks within the French parliament is one key reason for the stabilisation of the political regime under the Fifth Republic. This article starts with precise measures of the extent to which patterns of cohesion have changed throughout the twentieth century in France. It then moves to explain why cohesion has improved with the new regime of the Fifth Republic despite the change to a single member district electoral system and the direct election of the president. Both are generally expected to threaten cohesion. The two-round electoral system and semi-presidentialism prove, however, to be important explanations of the emergence of strict discipline in the French parliament.