A global surge in hydropower dam construction is underway, with at least 3,700 major dams, each over 1 MW in capacity, either planned or under construction, mainly in emerging economies. These dams are expected to increase global hydroelectric capacity by 73%, reaching about 1,700 GW. However, this expansion will not meet rising electricity demand, nor will it significantly reduce greenhouse gas emissions or resolve social conflicts. It is also projected to reduce free-flowing large rivers by 21%. There is an urgent need to assess the social, economic, and ecological impacts of this construction boom. The global energy demand has risen sharply, with electricity production increasing by 72% between 1993 and 2010, and expected to rise by 56% by 2040. Over 1.4 billion people still lack electricity access, particularly in rural Sub-Saharan Africa and South Asia. Renewable energy sources, including hydropower, are becoming increasingly important, with hydropower contributing 80% of renewable electricity production. Over 37,600 dams over 15 m in height are in operation worldwide, with 32 countries relying on hydropower for over 80% of their electricity. The Rio+20 targets require countries to meet growing energy demand using Kyoto-compliant resources, driving further investment in hydropower. Currently, 22% of the world's technically feasible hydropower potential is exploited. The current dam construction boom is unprecedented in scale and extent, following a period of stagnation. The inventory of future hydropower dams includes those currently planned or under construction, with data from over 350 sources. This compilation focuses on dams designed for hydropower, excluding those primarily for water supply, flood control, navigation, and recreation. It also excludes small dams (<1 MW). The data compilation allows for identifying future hotspots in hydropower development, calculating the number of dams in major river basins, and estimating the cumulative impact on river fragmentation. This information provides a foundation for future studies on regional conflicts and trade-offs between hydropower benefits and ecological, social, and economic impacts.A global surge in hydropower dam construction is underway, with at least 3,700 major dams, each over 1 MW in capacity, either planned or under construction, mainly in emerging economies. These dams are expected to increase global hydroelectric capacity by 73%, reaching about 1,700 GW. However, this expansion will not meet rising electricity demand, nor will it significantly reduce greenhouse gas emissions or resolve social conflicts. It is also projected to reduce free-flowing large rivers by 21%. There is an urgent need to assess the social, economic, and ecological impacts of this construction boom. The global energy demand has risen sharply, with electricity production increasing by 72% between 1993 and 2010, and expected to rise by 56% by 2040. Over 1.4 billion people still lack electricity access, particularly in rural Sub-Saharan Africa and South Asia. Renewable energy sources, including hydropower, are becoming increasingly important, with hydropower contributing 80% of renewable electricity production. Over 37,600 dams over 15 m in height are in operation worldwide, with 32 countries relying on hydropower for over 80% of their electricity. The Rio+20 targets require countries to meet growing energy demand using Kyoto-compliant resources, driving further investment in hydropower. Currently, 22% of the world's technically feasible hydropower potential is exploited. The current dam construction boom is unprecedented in scale and extent, following a period of stagnation. The inventory of future hydropower dams includes those currently planned or under construction, with data from over 350 sources. This compilation focuses on dams designed for hydropower, excluding those primarily for water supply, flood control, navigation, and recreation. It also excludes small dams (<1 MW). The data compilation allows for identifying future hotspots in hydropower development, calculating the number of dams in major river basins, and estimating the cumulative impact on river fragmentation. This information provides a foundation for future studies on regional conflicts and trade-offs between hydropower benefits and ecological, social, and economic impacts.