The project “EfSoLaw” aims to advance the understanding of the performance of the EU's multilevel system through a longitudinal analysis of the nature and effects 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 increasingly takes 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 about why member states and EU institutions chose either soft or hard law to govern. As a first step, a new comprehensive database was built to investigate the proportion of EU soft and hard law in seven different policy areas (Common Foreign and Security Policy, Financial Regulation, Food Safety, Pharmaceutical Regulation, Police and Judicial Cooperation, State Aid and Sustainable Agriculture) over 15 years (2004-2019). Second, the project explores how and why EU soft law is implemented at the domestic level through in-depth case studies and a survey in central administrations and courts in France and Germany. In a third step, we investigate when and why soft law feedbacks into EU policy-making. The project makes it possible to employ a multidisciplinary perspective and country expertise by combining a team of German and French political science and legal scholars.