The importance of international law has grown in an increasingly global world. States and their citizens are interconnected and depend on each other to enforce and comply with international law to meet common goals. Despite the expanding presence of international law, the question that remains is whether international law matters. Do individuals comply with international law? And when they comply, do they comply because they fear penalties or because they desire to behave appropriately? This Article presents results from a randomized field experiment designed to investigate these questions. Major findings include that roughly one in seven international actors is willing to violate international law and that the existence of penalties actually motivates some actors to break international law in greater numbers. In the first and largest global field experiment to date, this Article not only advances the scope of research methods generally, but also marks new ground by providing theoretical insights into the central questions of international law.