Overfishing threatens the viability of high seas living resources. Furthermore, controls to prevent overfishing are inadequate. Illegal, Unreported and Unregulated (IUU) fishing is a product of overfishing and affects all marine fisheries. Southern Ocean fisheries have been particularly targeted by IUU fishing. The efforts of the Convention for the Conservation of Antarctic Marine Living Resources Commission and the Australian government to adopt complementary measures to deter IUU fishing in the Southern Ocean form the basis of this study, although the examination is conducted following a comprehensive review of the legal and other factors contributing to the development of IUU fishing as well as the applicable international law.