While the law is often highly harmonized at EU level, the ways in which it is realized in the various national courts are not. This thesis looks at enforcement through damages claims for violations of EU public procurement rules. Despite important recent amendments to the procurement remedies regime, the damages provision remains indeterminate. The legislative inertia pressures the CJEU to give an interpretation and raises the question as to how the Court should deal with damages. The requirements on damages claims are clarified under both general and public procurement EU law. The action for damages is conceived as a legal process which incorporates the national realm. Therefore, a comparative law part (covering England, France, Germany and the Netherlands) examines national damages litigation in public procurement law. A horizontal discussion of the legal issues which structurally frame damages claims is provided. The remedy of damages is analyzed as a bundle of rules and its constitutive and quantification criteria are studied, thereby refining the the Member States’ common conceptual base of damages claims. Functionally, the lost chance emerges as a compromise capable of mitigating the typically problematic nature of causation and uncertainty in public procurement constellations. An adjudicative approach to damages in EU law is developed through Member State liability and the procedural autonomy doctrine. Member State liability is construed as a form of constitutional liability which is distinct from damages arising under the 'effectiveness’ postulate of procedural autonomy. Procedural autonomy as currently used is legally indeterminate and inadequate from the point of view of procedural theory. The thesis proposes to sharpen the effectiveness test in three dimensions: material, based on the intrinsic connection between enforcement rules and substantive law; vertical, in delimiting the spheres of influence of national and EU courts; and in terms of institutional balance vis-à-vis the EU legislator.