This is the first of five policy papers in a series for the EU-funded TransCrisis Horizon 2020 research project that directly address backsliding as a possible crisis for the EU. Taken together, the five papers investigate and analyse the causal links between transboundary crisis management and backsliding in EU member states. The first paper defines backsliding and explores empirical patterns of backsliding across the EU. The second, third and fourth papers analyse three forms of backsliding that are particularly contentious and involve potential problems for the EU: the rule of law (constitutional safeguards and independent institutions), corruption (including corruption control) and equality (gender, race and disability). Each of the three papers assess the extent of and causes of backsliding, and consider far it might be a problem for the EU. The fifth paper asks whether backsliding as such represent a crisis for the EU, and what policy options and tools the EU has for managing backsliding.