The United Nations Educational, Scientific and Cultural Organization (UNESCO) Conference at its thirteenth session in November 1964 resolved to make 1965-1974 as International Hydrological Decade (IHD). Its main purposes were to coordinate the development of research in the field of hydrology and to increase the knowledge of science in all countries, thus enabling these countries to evaluate their resources for the benefit of mankind. The IHD was officially inaugurated on January 1, 1965. The National Committee of the Republic of China for the IHD was organized in 1965. A number of programs to strengthen hydrological research in Taiwan were accomplished. In commemoration of this emphasis, a set of commemorative postage stamps with water circulation as its central design was released on June 6, 1968, the Water Conservancy Day in our country.