This article analyses the role of third parties in the enforcement of the Foreign Subsidy Regulation (FSR). It focuses on competitors, customers, and suppliers – market participants directly affected by distortive foreign subsidies – as a special form of third parties. Third parties might have a vested interest in the enforcement of the FSR against subsidy beneficiaries because they could be affected by the distortive effects of foreign subsidies. Third parties may also be of value in the FSR enforcement through detection, involvement in Commission procedures, or through private enforcement measures. Consequently, the article investigates complaints, participation in Commission FSR proceedings, judicial review, and private enforcement in national courts. It draws some conclusions and comparisons with third party enforcement in other areas of EU law, notably EU State aid, competition, merger control and trade law, but it works out the unique approach for third party enforcement of the FSR. Despite the FSR’s gap-filling function, it deviates significantly from third party enforcement in other areas of EU law, as it only provides limited options for such third-party enforcement.