While understanding interest group systems remains crucial to understanding the functioning of advanced democracies, the study of interest groups remains a somewhat niche field within political science. Nevertheless, during the last 15 years, the academic interest in group politics has grown and we reflect on the state of the current literature. The main objective is to take stock, consider the main empirical and theoretical/ conceptual achievements, but most importantly, to reflect upon potential fertile future research avenues. In our view interest group studies would be reinvigorated and would benefit from being reintegrated within the broader field of political science, and more particularly, the comparative study of government. The study of interest group politics-that is the organisation, aggregation, articulation, and intermediation of societal interests that seek to shape public policies-is a relatively small field within political science. There is no special journal devoted to interest group studies, and mainstream political science journals publish less on interest groups than they do on other areas of political science such as electoral, legislative, and party politics. 1 This phenomenon is not due to interest group scholarship being less advanced or less sophisticated than the other sub-fields. It is largely an artefact of size: fewer scholars work in the group area than in party politics or policy studies. There are also more substantive reasons for the paucity of interest group research: several conceptual, methodological and disciplinary barriers militate against the accumulation of knowledge. Nevertheless, during the last 15 years, the academic interest in group politics has grown. This is evidenced by numerous empirical studiesqualitative and quantitative-within the fields of European Union studies, comparative European politics, and American politics. In recent years, the

International audienceDrawing on a survey of 800 business associations, the article seeks to explain why interest groups lobby the EU institutions and what groups maintain contacts with them. Rooted in organizational theory, it argues that four main dimensions influence access patterns — institutional context, resource dependencies, interest group organization, and strategic choices. The empirical analysis demonstrates that all dimensions are relevant. Nonetheless, contacts between EU policy-makers and interest groups display only a few general traits: they are shaped by the political mobilization of groups in response to EU regulation, the division of labour among EU and national associations and the importance of organizational resources. Beyond these general influences, the interactions vary profoundly in the segmented institutional context

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and European Union (EU) trade associations as well as thirty-four large firms. The argument is that the multilevel governance approach to European integration captures the realities of EU interest intermediation better than neofunctionalism and intergovernmentalism. The article suggests that the strategies of interest organizations depend mainly on their location in the EU multilevel system and on their governance capacities. I distinguish two kinds of governance capacities: negotiation capacities and organizational resources. The analysis proceeds in the following steps: After outlining the three theories of European integration and presenting their implications for interest groups, a brief overview of the relative importance for interest organizations of EU and national institutions over time is provided. Then, cluster analysis techniques serve to identify types of interest groups according to their lobbying strategies in the multilevel system: niche organizations, occasional players, traditionalists, EU players, and multilevel players are distinguished. The composition of these clusters and the characteristics of their members support the multilevel governance approach and indicate that multilevel players have greater governance capacities than organizations in the other clusters.

This article outlines both the overall structure of the INTEREURO Project (Comparative Research on Interest Group Politics in Europe) and the theoretical foci, research activities and data sets generated by its several modules. We provide this description for two purposes. First, it provides a necessary backdrop for understanding the remaining essays in this special issue. Importantly, we do not believe that the methodological challenges we faced are unique to the INTEREURO Project. Rather, they characterize any large-N research project on interest representation. Thus, we hope that these articles based on the INTEREURO Project are useful to a broad range of scholars. Our second purpose is to describe for the wider community of interest organization scholars the INTEREURO Project and the data generated thereby.