On April 2, 2015, the International Tribunal for the Law of the Sea (ITLOS or Tribunal) rendered an advisory opinion on the rights and obligations of flag states and coastal states regarding illegal, unreported, and unregulated (IUU) fishing within the exclusive economic zone (EEZ). ITLOS confirmed that the full Tribunal—not just its Seabed Disputes Chamber—has jurisdiction to render advisory opinions, a matter of controversy that had previously been untested. The Tribunal also held that under the 1982 United Nations Convention on the Law of the Sea (UNCLOS or Convention), flag states have a “due diligence” obligation to ensure that vessels flying their flag do not engage in IUU fishing activities, and that the flag state may be held liable if that obligation of due diligence is breached. In addition, the Tribunal clarified that where fisheries competence has been transferred from a state to an international organization, it is the organization, not the flag state, that may face liability for a failure to have taken adequate measures to prevent IUU fishing. Finally, the Tribunal confirmed that coastal states have a duty to consult and cooperate with each other in the sustainable management of shared stocks and highly migratory species.