Public procurement law is still divided into two parts: Above the EU thresholds, numerous EU directives give concrete form to national law and grant bidders subjective legal positions that can be enforced in court. Below the EU thresholds, the legal situation under budgetary law remains unchanged. This dichotomy is also reflected in the level of legal protection: bidders in a procurement procedure below the EU thresholds are virtually deprived of legal protection under national law. As this dissertation shows, however, Union law is having an impact in this area as well and is significantly improving the legal protection situation of bidders. The influence of EU law on national public procurement law and the specification of this influence by the case law of the EU and national courts is systematically elaborated by the author on the basis of four case constellations.