The conservation and management of fisheries on an international level is no longer a task shared by States and international organizations. The ongoing degradation in the health of the world’s fish stocks has rallied private actors to the cause. One of the more significant facets of contemporary global fisheries governance is the emergence of private fisheries certification initiatives, the most prominent of which in terms of uptake is the Marine Stewardship Council (MSC). Whereas the impact of private fisheries certification on domestic regulation has been documented in literature, there has been little research into the interactions between the MSC and inter-governmental Regional Fisheries Bodies (RFOs). The chapter will address two MSC certified fisheries, namely South Georgia Patagonian toothfish longline and Maldives pole and line fishery, which are situated within the area of competence of the Commission for the Conservation of Antarctic Marine Living Resources and the Indian Ocean Tuna Commission respectively. The chapter aims at unpacking the reciprocal interactions between the MSC and the aforementioned RFOs in terms of standard setting. Indeed, it will be argued that private certification by the MSC presupposes and grafts onto pre-existing international legal rules on fisheries. At the same time, the operation of the MSC has evolved into a template upon which international legal rules may be modelled. The chapter also seeks to measure the extent to which the operation of the MSC within RFO areas impacts on the effectiveness of international law. The dual hypothesis is put forth that the operation of private certification may prompt or lock in compliance with international fisheries law by States, who want to guarantee the benefits of certification for their industry.