Are European Court of Justice judges biased towards their member states?

The Court of Justice of the European Union’s rulings significantly influence the European Union’s single market, the trajectory of European integration, and the efficacy of the rule of law in Europe. However, due to the Court of Justice’s practice of delivering decisions per curiam without publicly available votes, the impact of individual judges’ biases on case outcomes remains largely unknown. This article explores whether the Court of Justice’s judges are biased towards their appointing member states. I provide evidence across multiple datasets that when a judge receives an observation ( amici curiae brief) from their appointing member state, the judge’s panel is more likely to rule in favor of the member state’s position. This result holds irrespective of whether a judge is serving as the rapporteur (judgment-writer).