The paper presents a new approach to EU governance by stressing the interdependence of governance and integration. It suggests that EU governance is not just shaped by the emerging properties of the EU polity but has a strong impact both on system formation at national and European level. It is a process of mutual structuration which is likely to affect the integration and coherence of member state systems up to a point where European ‘good governance’ may threaten the governability and democratic quality of established national systems. The paper goes on by presenting an analytical model to assess in a systematic way why and when EU governance may qualify as stumbling stones for member state coherence or stepping stones for transnational integration. A preliminary test of this analytical model comes to the conclusion that EU governance has the effect of opening a transnational polity space which, however, has so far not produced any visible dis-integrative effects at the national level. In view of the long time horizons for social change, the paper recommends thorough comparative research to take a closer look at the interdependence of EU governance and system evolution.