Reef Builder was a partnership between The Nature Conservancy Australia (TNC) and the Australian Government and has supported Australia’s largest marine restoration initiative to date. This $20 million Program sought not only to restore near-extinct shellfish reefs at 13 project geographies across southern Australia, but also to provide much needed economic stimulus to regional and metropolitan economies impacted by the COVID-19 pandemic, and those devastated by the 2019 bushfires. Shellfish reefs, created when millions of oysters and mussels settle onto each other, are natural solutions to some of our greatest conservation challenges. They improve coastal water quality, boost fish stocks, provide homes for a diverse range of sea life, generate regional employment, and protect Australia’s coastal communities and shorelines from coastal erosion. Once expansive across Australia’s estuaries and bays, most of these natural habitats have been decimated since the 1800s by years of commercial harvesting, sedimentation, pollution, introduced species and disease. Fewer than 8% of our natural shellfish reefs remain acrosssouthern Australia’s coastline today, rendering them functionally extinct. Delivered between 2021 and 2023 in collaboration with government, natural resource management organisations, industry, First Nations groups, community groups, recreational fishers and universities, Reef Builder has restored over 40 hectares of lost shellfish reefs across 13 projects spanning Western Australia, South Australia, Victoria, Tasmania, New South Wales and Queensland. These reefs have been seeded with 30 million native oysters and mussels to initiate the restoration process and their ecological development monitored post-construction. This restoration work generated 425 new employment opportunities for local communities, which was 2.5 times greater than the anticipated employment target. These jobs were primarily within small-to-medium enterprises, a vital driver of our economy, and the majority of people employed worked locally. Engaging community also underpinned the success of the Program, with 185 stakeholder and community events, involving participation from over 5,200 community members. This included over 300 volunteers, who contributed 2,900 hours to the onground delivery of the Reef Builder outcomes, such as through TNC’s Shuck Don’t Chuck shell recycling initiatives, shellfish gardening, and water quality and fish monitoring. Combined with the shellfish reef restoration initiatives delivered by TNC and partners since 2015, a total of 21 shellfish reefs covering a restoration area of 62 hectares have now been restored across southern Australia. This is a considerable advancement towards TNC’s broader goal of rebuilding 60 reefs across Australia by 2030 and recovering 30% of these lost habitats. Reef Builder has demonstrated that the restoration of shellfish reefs at a national scale is possible, and that the flow-on benefits to people and nature are significant. This Reef Builder Summary Report provides an overarching synthesis of the key ecological and socioeconomic outcomes of the Program, and includes a selection of project case studies which help share the story of our three year delivery journey. It also includes key lessons learnt, as well as anticipated next steps towards 2030. Accompanying this broad overview is a more detailed Reef Builder Monitoring and Evaluation Report (10.5281/zenodo.11516296), which summarises key analyses of the Program data, and assesses level of success in achieving the Program targets and goals.