In this report, the World Bank assesses factors likely to determine marine protected areas’ (MPA) success and identifies opportunities for the Bank and its partners to scale up MPA implementation to meet global conservation targets, such as those set at the World Summit on Sustainable Development. The report focuses on how best to capture the potential benefits of MPAs for helping the world’s poor, while addressing the sociocultural and political realities of restricting access to the sea and regulating what has traditionally been considered common property.