Abstract This article reviews the evolution of subsidiarity as a constitutional principle within the case law of the European Court of Justice. It argues that, to date, discussion of subsidiarity as a judicial principle remains narrowly focused on its impact as a restraint on the Union legislature. In an effort to steer debate in another direction, this article revisits and supports arguments in favour of applying subsidiarity as a brake on the Court's own interpretative functions. Thereafter, it isolates the Court's interpretation of the Treaty free movement provisions as an empirical example to test this underdeveloped dimension of subsidiarity.