ABSTRACT. We examine new dynamics of privatization and collective action in common pool resource situations facilitated by the nonstate multistakeholder institutions of the Marine Stewardship Council (MSC), the global leader in sustainability certification for wild caught seafood. Through a review of the literature and two case studies of fishing cooperatives in Baja California Sur, Mexico and on Fogo Island in the Canadian Province of Newfoundland and Labrador (NL), we advance two interrelated arguments. First, certification and eco-labeling institutions privatize fisheries governance in largely unexamined ways through the injection of new forms of exclusive rights or privileges into common pool resource situations already complicated by access and property privileges, creating conditions for confusion and conflict as well as cooperation. Second, the MSC whole stock definition of sustainability places greater demands on certification clients for engaging in collective action by encouraging coordination over all social extractions from targeted fish stocks. Although rules encouraging collective action in common pool situations militate against the narrow private capture of certificate and eco-label rights, they also undermine the ability of small-scale and community-based fisheries that are embedded in larger unhealthy fishery contexts to acquire the right to the MSC stamp of sustainability. We conclude that MSC certification and ecolabeling create new institutions of private property rights and collective action, which can result in exclusionary practices, inclusionary collective action, or both. Much will depend on the specific common pool context and history of the fishery.