In response to the global fisheries crisis new governance models have been developed. In this thesis, I study one such model, Fishery Improvement Projects (FIPs), that have increased in numbers and importance globally, yet received little scientific attention. Alongside seafood certifications schemes, FIPs have been developed to meet the growing demand for sustainable seafood. By employing a multi-stakeholder approach, these projects aim to use the power of the private sector to improve fishery management and fishing practices. However, processes within these projects, and how they function as an instrument of change to improve fisheries, have been particularly understudied. This thesis explores the potential benefits and challenges of FIPs as a private governance approach for achieving sustainable fisheries. Paper I presents the first global systematic description of FIPs governance processes by examining reported actions, the actors involved, and their achievements. It reveals that FIPs have influenced both governmental policy (e.g., through management plans and new governmental management bodies) and industry-led practices (e.g., traceability programs and gear changes). It also demonstrates that FIPs include a diversity of actors, although fishers and retailers are relatively absent in FIP actions. The paper proposes that FIP actions and outputs can be categorized as either complementary or reinforcing of state regulations. Paper II contributes with an in-depth case study of the blue swimming crab FIP in Indonesia. By using the lens of institutional entrepreneurship, the study provides a historical analysis of the value chain from village fishers in Indonesia to importers in the US. It describes the entrepreneurship behind the FIP’s establishment and its institutional interventions, as well as addresses why these have been unsuccessful in changing behaviours of fishers and traders to increase the ecological sustainability. The paper expands on the theoretical understanding of institutional entrepreneurship. Paper III presents an overview of how fishers participate in FIPs based on data from FIP implementers world-wide. Fishers are mostly involved in data collection efforts and less involved in developing FIP workplans and objectives indicating that they are not involved in the early development process of the FIP. The lack of overall benefits for fishers together with limited capacity and skills within projects were identified as the main barriers to have meaningful fishers' participation, flagging some critical challenges for the FIP model. Finally, Paper IV uses a literature review of the social embeddedness theory within fisheries literature to explore how social context influences economic actions in fisheries trade. The paper emphasizes the importance of how social identity (e.g., ethnicity) shapes market access and how the level of (dis)trust between actors impacts trade strategies. It discusses the implications of these findings for research and implementation of FIPs and other market-based interventions. Together, these four papers contribute with novel empirically grounded understandings of FIPs, which is relevant for the growing literature around private governance as well as for the global community of practice within the sustainable seafood movement. These papers provide important insights into the ongoing debate about effective governance approaches for improving the sustainability of fisheries for both people and ecosystems.