Article 100 of the UN Convention on the Law of the Sea requires parties to “cooperate” against maritime piracy, but how this cooperation is to be achieved is undefined. Enforcement is a public good—creating uncompensated benefits for others, thus suffering from free rider problems. The analysis in this article explains why more pirates captured are released than prosecuted, why the United Nations and the International Maritime Organization are seeking to reduce enforcement costs, why some in the shipping industry want to apply the 1988 Convention Against Terrorism at Sea, and why still others want to move prosecution of pirates from national courts to an international court.