In this volume, well-known authors deal with current legal issues at the interface between procurement and antitrust law, as well as social security law. The background to this is the case law of the Court of Justice of the European Union (ECJ). The decision in the Oymanns / AOK case by the ECJ was a bang with far-reaching consequences for German social security. In the future, social security institutions will have to advertise services that they receive from third parties across Europe more frequently. This gives rise to numerous follow-up questions that will occupy the German courts in the near future. In addition to the direct consequences of the decision in this case for the German social security systems, the articles also discuss the influence of European antitrust law on German social security institutions, including the question of whether these companies are in Article 101 et seq. Of the TFEU and whether they can be privileged if necessary.