This four-year project funded by the German Research Council analyses conditions under which states do (not) comply with law beyond the nation-state. It develops hypotheses for explaining non-compliance from the existing literature and tests them systematically for the area of European law. We therefore draw on a database which includes almost 10,000 infringements of EU member states against EU law in the last 30 years. The large number of cases, which vary according to policy sectors, memberstates, type of legal acts as well as type of violation, allows for the first time to actually test explanatory factors by using quantitative methods. How effective aresanctions for deterring states from violating law beyond the nation‐state? To which extent is (non-)compliance a matter of state capacity? Does the perceived legitimacy of a rule matter for the actual level of compliance? What is the role of supranational institutions like the European Commission or the European Court of Justice for monitoring and enforcing compliance? Do non-state actors effectively act as compliance proponents or opponents? The quantitative analysis has already shown that capacity-related variables like bureaucratic efficiency have a lot of explanatory power for the level of non-compliance in the EU. Qualitative case-studies are conducted in order to complete the quantitative approach and to disentangle the underlying causal mechanisms which result in (non-)compliance with a rule. Cases have been selected, on the onehand, by analyzing two compliance ‘laggards’, who both infringe frequently on EU law, but perform differently on a number of explanatory factors (Greece and Italy) and, on the other hand, by analyzing one compliance ‘leader’ and one compliance‘laggard’, which vary in their propensity to violate EU law, but perform similarly onmany explanatory variables (United Kingdom and France). The comparative casestudies specifically draw on the implementation of EU environmental directives. Apart from completing the findings of the quantitative analyses, the comparative case studies shall also analyze to which extent (non-) compliant behavior can be explained by mechanisms of learning and persuasion, since the corresponding hypotheses are hardly quantifiable. Finally, the project will explore interaction effects between the different compliance mechanisms.