This study evaluates the role of law in the transboundary environmental governance of the Baltic Sea with regard to eutrophication, on the basis of theories on resilience in social-ecological systems. The scientific discourse on resilience in social-ecological systems provides theories on effective governance of complex environmental problems with nonlinear causal connections. Hence, these theories forms a useful tool in assessing how environmental law can address the challenge of such complexity. The applicable law in the Baltic Sea area reflects resilience features such as adaptability, flexibility and redundancy within the legal structure. The legal structure for the Baltic Sea is dynamic and stretches over many levels of governance. The legal instruments moreover include significant elements that provide for participation at different levels, which contribute to the resilience features. However, law is based in a number of general principles connected to the rule of law and the function of law as a foundation for stability in human interactions. These principles are important since they are directly linked to enforcement, monitoring and control. While the legal structure in the Baltic Sea provide for effective governance and social-ecological resilience, the resilience features reflected in law do not always appear as far-reaching as suggested by resilience theories, much due to these legal principles. However, because of these principles law can push for other measures contributing to social-ecological resilience, which might not have been accomplished otherwise. This is a doctoral thesis in environmental law at Stockholm University, Sweden 2017.