Failing to amalgamate communes, the French government has made a number of attempts to strengthen cooperation between them. The scope and the number of local institutions designed for cooperation has strongly increased, French territory being now divided into thousands of Communautés (specific regimes of cooperation), whose budget and expertise are considerably developped. This communication, based on socio-historical investigations on different cases (Lille, Chambéry, Nantes, Marseille), aims at giving a global interpretative framework to the development of intermunicipal institutions : the dissemination and development of Communautés has not widened the scope of actors involved in public actions but supported the capture of policy-making by a small group of political elites, namely the mayors. The quantitative ""success"" of cooperation is the result of mayors' efforts to neutralize the reforms and control their implementations, what we call " smokescreen success ". The paradox of intermunicipal power, stronger but less accountable, is just an apparent one : " communautés " have developped precisely because they are not democratic. Finally, the ""consensus"" prevailing in communautés' political regulation fails to integrate peculiar social interests, due to the preferred development of corporative ties among political elites and the simultaneous weakening of the traditional arenas of the democratic expression, such as municipal Council, political parties and associations.