Research on European legal integration has focused on the impact of the process of integration on national courts and the impact of courts on the same process. Both lines of research, however, have positive theories of the functioning of judicial cooperation in the EC judicial system, which often times remain underspecified. The models used to account for it make different assumptions as regards the preferences of judges, the structure of adjudication and render different explanations of the practices of referral and precedent among courts. My aim here is to first elaborate on three such models –the legal model, the bureaucratic mode and the team model- and then proceed to some empirical tests. I concentrate on the effects of hierarchy on judicial cooperation. After reviewing the evidence put forward by previous studies of legal integration and offering some new evidence, I conclude that the practices of judicial cooperation seem to be explained by the predictions of the team model. National courts take their role as “primary community courts” and use the ECJ as a guidepost to resolve complicated EC law issues. Moreover, higher courts in member states do not seem to be more reluctant to cooperate with the ECJ than lower courts in the application of EC law. The results shed some light on some proposals to reform the EC judicial system.