The paper investigates the opportunities and the limits of economic analysis in international economic law. Based on a legal theory approach, it highlights the different epistemological statements in law and explores where and how social sciences, and especially economics, may play a role in law-making (external view) and law-application (internal view). International Economic Law is in special need of economic insights (economics as a subject-matter). Economics as a methodology (and its empirical insights) can also be used to explain noneconomic issues in international economic law, such as treaty negotiations. Examples from trade and investment law highlight the need for economic analysis in international economic law as well as its limits.