For the purpose of these Guidelines on Public Participation in EIA in the Mekong Region (‘the Guidelines’), the term Environmental Impact Assessment (EIA) has been used in its generic sense. This term takes into account the broad nature of the modern application of EIA, as most countries adopt a definition of EIA that includes an assessment of all significant impacts (direct, indirect and cumulative) on people, the economy, and the environment. While national legislation may refer to slightly different terms, such as Environmental and Social Impact Assessment or Environment and Health Impact Assessment, these are viewed synonymously as variants of EIA. EIA provides a clear reminder of the need for the assessment process to be as complete as possible when considering and assessing all the significant impacts from a project. EIA should focus on the significant impacts of proposed projects. This will allow for the most efficient use of limited resources to focus on issues of concern and not “all” impacts, many of which are insignificant or of minor concern.EIA procedures are in place in all Mekong region countries – Cambodia, Laos, Myanmar, Thailand, and Vietnam – but critical gaps remain in its effective implementation. These gaps involve a number of factors, including the overall quality of assessments, consideration of alternatives, monitoring and compliance, and meaningful stakeholder engagement, among others. Such challenges result in poorly-designed projects with adverse social and environmental impacts; project delays and conflicts with communities, leading to higher costs for project developers; and an undermining of the long-term sustainable development in the region.