This article considers the impact of subsidiarity on the role of the Court of Justice as a policy actor. It considers briefly the meaning of the subsidiarity principle in the EC Treaty, and examines how the Court has engaged with this principle. Both the Court’s use of subsidiarity as a means of reviewing the other institutions, and its sensitivity to the principle in relation to its own interpretative role are analysed. The problematic tension between the institutional constraints of the Court’s role and methodology, and the requirements of the expanding culture of subsidiarity are explored.