On the threshold of post-modernism, the shape of ecumenism is in a process of change. It passes from a system to a form of networking. This article reflects on this process against the background of the question of the French sociologist of religion Jean-Paul Willaime whether ecumenism is out-of-date. According to Willaime, ecumenism has become a disordered pluralism. He only draws attention to the nihilistic and pluralistic character of post-modernism, but does not look at its aesthetic-mystic dimension. The history of western ontology shows three consecutive ways of experiencing reality: substance, system, and structure (Heinrich Rombach). Ecumenism has been developed as a system, in which unity predominates, but post-modern culture, with its priority to pluralism, challenges it to shape itself as networking and to think about unity in more sacramental and in more juridical terms.