Three-quarters of the poorest households in the world live in rural areas and are dependent on shared access to natural resources for their food security and livelihoods.However, certain features of these natural resources make their management problematic, especially the high degree of interdependence among resource users, creating incentives to overuse resources and underinvest in their sustainability. Hence, much research has focused on the role of collective management of natural resources in supporting sustainable rural livelihoods. This focus has also influenced the design of rural development and conservation programs, assuming that local people who use and rely on natural resources are in the best position to manage them. Yet interventions to promote collective management of natural resources have often failed due to excessively top-down, prescriptive approaches that ignore local institutional contexts. Hence there is a need to understand better the processes of local collective action.These issues are especially relevant in Bangladesh's coastal zone, where pressure on land, water, and other natural resources is intense and increasing. The coastal zone plays an important economic role through crop production and aquaculture, and supports the environmentally-significant Sundarban mangrove forest. Yet it is also highly vulnerable, facing problems of salinization, waterlogging, flooding, riverine erosion, erratic rainfall, sealevel rise, and cyclone-related disasters. Development interventions in this zone have also had mixed consequences. The complex, interrelated nature of land, water, fisheries, forests, and infrastructure, the high degree of interdependence between resource users, and the shared exposure to natural hazards and climate trends mean that local processes of collective action play a crucial role in sustaining lives and livelihoods.The aim of this research was to explore the nature and role of local collective action in managing natural resources and enhancing the livelihood security of rural households and communities in coastal Bangladesh. A version of the Institutional Analysis and Development (IAD) Framework was used. This provides a general set of interrelated variables to systematically examine a diversity of cases, while allowing for different theoretical explanations in each case. The elements of the Framework are: (1) contextual factors (attributes of resources, attributes of resource users, and governance arrangements); (2) the action arena or "action situation", in which various actors, using their assets and governed by "rules in use", engage in patterns of interaction to pursue their goals; (3) the outcomes of this interaction for (a) resource status and trends, (b) ii livelihood assets and adaptive capacity, and (c) institutional arrangements and governance. The Framework can be applied to different scales and time-frames, encompassing both one-off local episodes of collective action and repeated, long-term interactions leading to institutional change.A qualitative, c...