This project aims to advance understanding of the performance of the EU multilevel system through a longitudinal analysis of the nature and effect of soft law. EU law affects governments and populations and has direct influence on the lives of citizens.With the governance turn and ever more complex decision-making in Brussels legislation takes increasingly often the form of soft law. The term captures instruments such as recommendations, guidelines or communications that do not entail jurisdictional control, but produce important legal and practical effects. Yet, we still know relatively little why member states and EU institutions chose either soft or hard law to govern. What is the proportion of EU soft law in different policy areas? When and why is EU soft law implemented at domestic level? Once implemented, when and why does it feed back into EU policy-making? Employing lenses of contemporary legal scholarship on soft law and political science insights on public policy analysis, this project investigates whether, and if so when, why and how soft law affects the performance of the EU multilevel system.