impact. Among all renewable sources, hydropower produces no air pollution and only a very small amount of greenhouse gases in comparison to other large-scale energy options [1,2]. Moreover, hydropower has a very high conversion efficiency of about 90% and a high energy payback ratio [3]. In addition, hydropower generation is carried out on both large and small scales due to its flexibility and reliability for integrating and developing energy systems. However, problems such as high capital costs and the resettlement of people occurred through large-scale hydropower projects. Table 1 shows the advantages and disadvantages of hydropower. Small hydropower systems can be installed on canals, dams, and run-of-river sites. In countries without integrated national electricity grids, small-scale hydropower provides reliable access to electricity, resulting in a higher quality of life at the household level [4]. In this way, the problem of unelectrified remote areas can be solved with the installation of small hydro systems [5]. For these reasons, hydropower is important to many countries. Thailand has many water resources in small and big areas that can be used to generate electricity. Therefore, a study on the water resources, current status of, potential for, and policy on hydro energy in Thailand is very important. Hence, this paper presents a review of the water resources, current status, and potential of hydro energy in Thailand. Future plans for using hydro energy in Thailand are also investigated