Friends of the Court? Why EU governments file observations before the Court of Justice

The preliminary reference procedure under which the Court of Justice of the European Union (CJEU) responds to questions from national courts regarding the interpretation of EU law is a key mechanism in many accounts of the development of European integration and law. While the significance of the procedure has been broadly acknowledged, one aspect has been largely omitted: The opportunity for member state governments to submit their views (‘observations’) to the Court in ongoing cases. Previous research has shown that these observations matter for the Court's decisions, and thus that they are likely to have a significant impact on the course of European integration. Still, little is known about when and why member states decide to engage in the preliminary reference procedure by submitting observations. This article shows that there is significant variation, both between cases and between member states, in the number of observations filed. A theoretical argument is developed to explain this variation. Most importantly, a distinction is made between legal and political reasons for governments to get involved in the preliminary reference cases, and it is argued that both types of factors should be relevant. By matching empirical data from inter‐governmental negotiations on legislative acts in the Council of the EU with member states’ subsequent participation in the Court procedures, a research design is developed to test these arguments. It is found that the decision to submit observations can be tied both to concerns with the doctrinal development of EU law and to more immediate political preferences. The conclusion is that the legal (the CJEU) and political (the Council) arenas of the EU system are more interconnected than some of the previous literature would lead us to believe.