ABSTRACT
The second chapter identifies two causal mechanisms linked to interest groups’ organisational structures on the horizontal axis: the integration and the isolation mechanisms. It argues that the departmental structure of interest groups critically affects who interest groups are in contact with and cooperate with (i.e. their ‘coverage’) at the European level. The ‘horizontal dimension’ refers to the departmental structure of groups and how departments cooperate and exchange information. The chapter borrows insights from classical organisational theory and organisational sociology and combines them with a comparative political science approach. It deduces two expectations for the horizontal dimension which are going to guide the empirical analysis in the sixth chapter.
