As a phenomenon accompanying European expansion, piracy and privateering spread globally, beginning in the sixteenth century. These activities, and their handling within transnational relations, shed light on several issues of modern international law, then under formation. They reflect different basic problems that both challenged and structured central aspects of legal relations on an international level: the transformation of ocean spaces into areas of colliding legal strategies, the use of privateers (‘legalized’ pirates) as a tool for extraterritorial expansion, the involvement of non-state players in international legal relations, the fragmentation of maritime sovereignty, and the application of international law to criminalize politi...