We examine how the EU can act as a great power in its own right even in the absence of military capability and how its institutional structure conditions this ability. We first theorize EU great power politics. Based on theories of corporate action, the EU constitutes a strong market power in its own right and a weak security power. While it is institutionally ill-equipped to purposefully mobilize its market power to pursue high-politics goals, its communitarized external relations may inadvertently challenge important security interests of other great powers. Second, we show that the EU acted as an inadvertent great power vis-à-vis Russia in its Ukraine policy which was primarily driven by the supranational decision-making apparatus and low-politics considerations, but engendered a bipolar power struggle with Russia over Ukraine. The risks inherent in EU inadvertent great power politics are deeply engrained in the EU's institutional structure and therefore difficult to mitigate.