Abstract: Isotope hydrology is a new discipline in earth sciences developed since 1950s. Its main target is to use isotope technique to solve various problems in hydrology. It is well known that isotope refers to those atoms whose numbers of proton are the same but whose numbers of neutron are different. Isotopes can be divided into two types: stable and radioactive. For stable isotopes, no radioactive decay has been found so far. But for radioactive isotope, there exists radioactive decay. Usually, the term "natural" and/or "environmental" isotopes were used for the two types of isotope mentioned above. The environmental isotopes commonly used in hydrology are: ²H, ³H, ³He, ⁴He, ¹³C, ¹⁴C, ¹⁸O, ³⁴S, ³⁶Cl, etc. It must be noted that for different types of water, such as sea water, lake water, river water and ground water, the isotope composition seems to be quite different but relatively stable, although the water chemistry varies greatly. Therefore, the isotope composition can be, to certain degree, regarded as the "finger print" and/or "DNA" of the water. Also for this reason, the isotope composition in the water and the isotope hydrology technique are widely used to solve various problems in water resources assessment and hydro environment evaluations such as the origin of water, the interaction of surface and groundwater, the rain off water, the degree of openness of a groundwater system, the intensity of water cycling, the pollution degree and the pollution source of a water body. In recognition of the importance of isotope hydrology, an isotope hydrology section has been established in the International Atomic Energy Agency (IAEA) and an isotope hydrology laboratory is set up simultaneously with advanced technique and equipment. Since late 1950s, a Global Network for Isotopes in Precipitation (GNIP) has been initiated jointly by IAEA and WMO (World Meteorological Organization) and all the data have been published since 1961. Recently, sponsored by IAEA/UNESCO, a similar global network for isotopes in the large rivers in the world is under the way to set up. It is of significant importance in promoting isotope hydrology development worldwide. In China, isotope hydrology studies can be traced back to the late 1960s. In the scientific investigation of water resources in Jolmo Lungma region, ²H and ¹⁸O were determined in snow and ice samples. Since then, ²H and ¹⁸O have been analyzed for precipitations in Beijing, Shanghai and East China by different researchers with great achievement. In 1988, Supported by the Ministry of Water Resources, the first 10 stations, for monitoring the isotopes in precipitation in China were established and now they have been included in the IAEA/WMO GNIP. At present, the total number of stations has increased to 30.Nowadays, water resources shortage and hydro environments degradation become more and more serious worldwide. According to the prediction by the World Bank, 2/3 world population will live in a serious water shortage environment if we follow the present water consuming model. At present, 70-80 billions of US dollars has been offered to the developing countries to alleviate the annual water resources shortage. The global demand for water resources will be doubled in the coming 15 years. For this reason, altogether 24 international organizations including IAEA are working on a World Project for Water Resources Assessment to reduce the global water shortage. "flood", "water shortage" and "water pollution" have become three main problems in China nowadays. Both the water shortages in the Heihe river region and the degradation of hydro environment in Taihu lake area have attracted great attention from the State Council. The isotope hydrology technique may play a particular role in solving these problems. All in all, opportunities and challenges co exist and it is a right time to expedite the development of isotope hydrology in China.