Scholarship on international law has undergone an empirical revolution. Throughout the revolution, however, shortcomings of the observational data that studies have used have posed serious barriers to reliable causal inference. During the same period, political scientists and legal scholars studying domestic law have increasingly employed experimental methods because they make it easier to make credible causal claims. Despite the simultaneous emergence of those trends, there have been relatively few attempts to use experimental methods to study international law. This should change. In this paper we present the first argument that the study of international law could uniquely benefit from the use of experimental research methods. To make this argument, we present data we have collected that illustrates why observational studies will often be unable to provide answers to many of the most important questions of legal scholars. After doing so, we provide guidance on how laboratory, survey, and field experiments can be used by legal scholars to research international law.