This ERC program addresses an unsettled political science problem, namely how does the shifting of policymaking competencies to higher levels of government affect the opportunities of societal interests to seek representation. On this issue two completely different theoretical expectations exist. One the one hand, the Madisonian view entails that shifting competencies upwards is a healthy antidote to the powers of specific interests that may dominate smaller polities. Multi-levelness may also provide political opportunities as it enables actors to make strategic venue shifts when they are unable to attract the necessary attention at one venue. On the other hand, shifting policymaking upwards may seriously restrict the opportunities for diffuse interests, undermine encompassing forms of interest representation, and increase the barriers for local groups to gain attention. Instead of creating opportunities for all, multi-layered systems may decrease opportunities and reproduce or reinforce representational bias. One of the reasons why the implications of multi-layeredness are so poorly understood is the fact that political science has not developed a proper understanding of what representational bias means; some scholars see bias in terms of mobilization, while others conceive it in terms of the strategic interactions between organized interests and policymakers.This ERC program will integrate theoretically, methodologically and empirically these different aspects of group politics, by taking explicitly into account the nature of multi-layered systems. The innovative character of it lies in the theoretical combination of mapping interest group community dynamics, with a more nuanced characterization of organizational form and an in-depth investigation of bias in terms of strategies.