To estimate accurate design quantiles considering statistical characteristics of hydrological data is one of the most important procedures in the design of hydraulic structures. While at-site frequency analysis estimates design quantile using observed data at a site of interest, regional frequency analysis (RFA) utilizes a number of sites included in a hydrologically homogeneous region. Therefore, RFA could provide a more accurate design quantile at ungauged site or sites with short observation period. In this review article, RFA is classified into stationary RFA and nonstationary RFA depending on the characteristic of hydrological data, and the basic concept, procedure, and application of each technique are explained in detail focused on the index flood method. Additionally, a review of the state of the art for RFA procedure is presented. This paper is finalized by describing the stationary regional rainfall frequency analysis over South Korea contained in the amendment of ┌Standard guidelines for design flood estimation┘ and various future study topics related to nonstationary RFA.