This chapter examines how the maritime domain has been appropriated as a space of international security operations by analysing the patterns of recent interactions at sea. It takes as its empirical case the western Indian Ocean, which for the past two decades has been subject to a range of security-related operations. From counter-terrorism in the wake of the 9/11 terrorist attacks to counter-piracy law enforcement and maritime security capacity-building in the late 2010s, the Indian Ocean has been a testing-ground for an evolving complex of international cooperation and burden-sharing. Using actual operations as the primary data source, the chapter maps how operations have evolved over time in the Indian Ocean.