The Belgian political system is generally portrayed as being closed for outsiders. In this article we ascertain how the system responded to the challenge of the new social movements. The Belgian political elite developed a response strategy, based on thematical openness and actorial closure. The issues of the new social movements were admitted on the political agenda, but the movements themselves were excluded from access to the decision making process. Only those actors were allowed which were willing to accomodate themselves to the traditional elite consensus, based on neo-corporatism, pillarisation and a politically passive population. Confronted with this elite strategy, the new social movements were able to fulfil their agenda function (bringing new issues on the political agenda), but they had little opportunity for introducing new cultural codes into the political decision making process. This lack of innovation enhances the legitimation crisis of the Belgian political system.