The accuracy and noninvasive nature of the doubly labeled water (DLW) method makes it ideal for the study of human energy metabolism in free-living conditions. However, the DLW method is not always practical in many developing and Asian countries because of the high costs of isotopes and equipment for isotope analysis as well as the expertise required for analysis. This review provides information about the theoretical background and practical aspects of the DLW method, including optimal dose, basic protocols of two- and multiple-point approaches, experimental procedures, and isotopic analysis. We also introduce applications of DLW data, such as determining the equations of estimated energy requirement and validation studies of energy intake.