The book highlights, with practical examples, the potential of isotope techniques in water resources development and management. It starts with a description of isotope characteristics as well as their relevance as tracers in studies on various stages of the hydrological cycle. The book covers applications of both environmental isotopes and injected tracers to surface water and groundwater bodies as well as their interrelationships.  In view of the importance of identification of groundwater recharge and recharge processes, due emphasis is given to this aspect of application of environmental isotopes. Role of isotopes in understanding groundwater contamination from natural pollutants like inland salinity, arsenic and nitrate is discussed with examples.