There is currently a widespread view that the EU is in crisis. This crisis is not only financial, but, most importantly, it touches upon the founding principles of the Union as set out in Article 2 TEU. Among them, a principle that has served as the cornerstone of European integration already from its early stages seems particularly threatened: the rule of law. This crisis has many facets. Because of undue interference with the judiciary, restrictions of media freedom, endemic corruption, or weak institutional capacities, some EU Member States present so grave deficiencies in guaranteeing the rule of law that their conformity with basic EU standards is seriously questioned. Although it is obvious that the EU cannot stay inactive in the face of such grave deficiencies, it remains unclear how potential responses fit with the overall EU constitutional framework. This research project contributes to this discussion by developing the concept of systemic deficiency in the rule of law and also by critically observing the on-going efforts to advance appropriate EU instruments to address the diverse challenges to the rule of law.