Intergroups are key components in the European Parliament's modus operandi, allowing members from different political groups to focus on specific political topics. Hitherto, the defining characteristics of Intergroups have not received much attention in academic literature. This article remedies this lack by conducting a study of Intergroups coached by network theory. It is shown that there are considerable variations between them. Though it is only parliamentarians who can be formal members, Intergroups may comprise a variety of different actors, and interaction is characterised by interests, non-hierarchical negotiations, easy communication lines and trust. Some Intergroups are targeted by interest groups to such an extent that a fusion nearly happens, whereas others do not receive any attention at all. Intergroups can have considerable impact by moulding ideas for new ‘wise’ policies. Finally, the analysis compares the function of Intergroups to that of the US Congress Caucuses and demonstrates that Intergroups bear resemblance in the way that they allow Members of the European Parliament to signal their preferences, exchange information and coordinate legislative initiatives.