Anastasia Telesetsky is an Associate Professor of Law at the University of Idaho College of Law] Cross-Posted at SHARES Blog. Sovereign nations have the right to extend their nationality to non-state actors who agree to adhere to national laws. But is there any broader international state responsibility associated with the granting of flag state status to known problematic non-state actors? Take the example of the South Korean flagged F/V Premier. This vessel licensed to the Dongwon company, the parent company of Starkist Tuna, was recently accused by Liberia of illegal fishing in the coastal waters of Liberia. In April, the Dongwon company settled with the government of Liberia for somewhere between one million and two million dollars. An interesting question has arisen over whether the government of Korea now has the obligation to list the F/V Premier as an Illegal, Unreported and Unregulated fishing vessel which would mean that the vessel would not be permitted to operate in regional fishery management areas such as those regulated by the Indian Ocean Tuna Commission. Within the IOTC waters, contracting parties and cooperating non-contracting parties are expected to demonstrate that vessels permitted to fish “have no history of IUU fishing activities or that, if those vessels have such history, the new owners have provided sufficient evidence demonstrating that the previous owners and operators have no legal, beneficial or financial interest in, or control over those vessels…” Granting the use of the flag and vessel registration are not part of an unconditional sovereign right. While Article 91 permits every State to “fix the conditions for the grant of its nationality to ships, for the registration of ships in its territory, and for the right to fly its flag”, this right is conditioned by Article 94 which provides that “[e]very State shall effectively exercise its jurisdiction and control in administrative, technical and social matters over ships flying its flag.” When read together, Article 91 and Article 94 suggest that among the necessary conditions for granting nationality or issuing registration is a State’s demonstration of effective jurisdiction and control over “technical matters” which would include vessel safety and “social matters” which in addition to labor practices might also include enforcing sustainable fishing practices. Healthy fisheries should be considered today a “social matter” since so many people globally depend on marine fisheries for basic animal protein and employment. A State is, of course, not required to fix structurally unsound ships or to staff fishing vessels with reliable fishing crews who understand conservation practices—but it is required to exercise control over those who might own unsound ships or practice unsound fishing practices. One easy way to exercise effective control over “problem ships” is simply to refuse to grant such vessels nationality or to allow registration of these ships. This post argues that States granting their nationality to or providing ship registration for any vessels that are 1) known or suspected IUU fishing vessels or 2) structurally unsafe cargo vessels violate erga omnes customary international legal duties as well as discrete treaty obligations.