As States and supranational actors increasingly employ economic sanctions to promote security objectives, a recent trend has focused on the regulation of commercial shipping activities. These maritime sanctions have restricted port access for designated vessels, banned the import and export of certain cargo classes, enhanced authorization for vessel inspections, and even justified vessel seizures. Critically, these techniques have also included targeted prohibitions on marine insurance covering designated vessels and cargo. Designed to frustrate sanctioned actors in their attempts to utilize maritime assets for malign purposes, marine insurance prohibitions thwart these efforts and also blunt the ability to generate revenue through legitimate commercial transactions. While such restrictions have been utilized to varying degrees in conflicts of the past, this technique has taken on new life in recent years as hybrid warfare tactics have gravitated toward sophisticated regulation of financial services and maritime infrastructure. Zeroing in on this phenomenon, this article explores marine insurance prohibitions as an instrument of contemporary economic warfare. It first offers historical context highlighting the political developments that led to their adoption as a geostrategic tool and then turns to recent application of marine insurance prohibitions targeting Iran and North Korea. Finally, it evaluates commercial reactions to these restrictions as shipping industry participants have politically mobilized, enhanced compliance initiatives, and attempted to shift sanctions risk in their business dealings.