<p>Two-thirds of fish stocks commercially fished on the high seas are either depleted or overexploited. Regional Fisheries Management Organizations (RFMOs) are key international actors having the legal competence to establish fishery conservation and management measures to improve the optimal and sustainable utilization of high seas fisheries resources. The literature suggests that their effectiveness is varied. While some RFMOs are making progress towards more sustainable fisheries, some are facing fish stock depletion. The literature indicates that organizational governance design and quality of implementation are central to the disparities. Thus far, while most of the discussion has focused on the effectiveness, and how to enhance the transparency of RFMOs, very little research has explored the designs of governance arrangements and implementation of RFMOs. Accordingly, this study contributes to the literature on governance arrangements and policy implementation of the high seas by offering in-depth case studies of the selected RFMOs. It employs qualitative methods to analyze data collected from semi-structured interviews with 24 actors (i.e., officials, delegations, and fisheries experts), as well as a collection of published and unpublished documents regarding three selected RFMOs. The three selected RFMOs are the Commission for the Conservation of Southern Bluefin Tuna (CCSBT), the Western and Central Pacific Fisheries Commission (WCPFC), and the South Pacific Regional Fisheries Management Organization (SPRFMO). The findings show that it is possible to apply Ostrom’s (1990) design principles to uncover how RFMOs can be designed for higher performance in governing high seas fisheries. However, adjusted and additional design principles are necessary to have a better understanding of the factors that contribute to sustainable high seas fisheries. For example, the design principles should include policy learning and adaption, particularly in the regional and global contexts, so as to address complexities and uncertainties. Furthermore, the research reveals a number of critical factors of RFMO policy implementation, such as strong political will and commitment, the availability of proper resources and coalitions. This study concludes with recommendations for policymakers of the RFMOs to better achieve their overarching objectives.</p>