"Over the past decade, strategic environmental assessment (SEA) has emerged as an increasingly important planning tool in the Greater Mekong Subregion (GMS). SEAs help policy makers better understand and integrate the environmental, social, and economic dimensions of strategies, plans, and programs. They are particularly important for power sector planning because the social and environmental impacts of such plans can be very significant and are often a major concern for governments and communities. Experience in the GMS, as well as further afield, shows that more sustainable and successful planning choices are made when these impacts are properly considered. The further uptake of SEAs in power sector planning in the subregion is needed to help seize opportunities that are emerging in the evolving energy landscape. Technological and economic transformations are making renewable energy an increasingly attractive and viable energy option for the GMS countries as elsewhere in the world. This trend aligns well with the national development policy priorities of all six countries as they increasingly emphasize green growth, climate change mitigation, and sustainable development. Using an SEA to support the preparation of power development plans can guide decisions on which energy generation options are optimal. It can ensure that these decisions are based on an understanding of the full economic costs and benefits to a country, rather than just shorter-term financial ones, as has traditionally been the case. An SEA enables planners to identify the potential negative impacts of different generation options. These impacts can lead to significant increases in costs and delays if not identified before the planning stage of projects. The integration of an SEA in power development planning enables energy sector investments to be quicker, more transparent, and more closely aligned to national development priorities. An SEA can also guide decisions on the most economical locations to invest in and help to ensure minimal impacts on communities and the environment. Since 2006, the Asian Development Bank (ADB) has been providing technical assistance through the GMS Core Environment Program (CEP) to help mainstream the use of SEAs in the GMS countries, including for power development planning. This publication outlines the key characteristics of SEA, discusses global trends in energy technologies and markets, and looks at how Viet Nam, with support from the CEP, has integrated SEAs into its power development planning process. It also identifies priority steps for further mainstreaming SEAs in power sector planning in the GMS countries..."