The development and practical implementation of isotope methodologies in water resources assessment and management have been proved to be useful. Isotope techniques can be applied to a wide spectrum of hydrological problems related to both surface and groundwater resources as well as environmental studies in hydro-ecological systems. The main aim of this book is to provide a review of basic theoretical concepts and principles of isotope hydrology methodologies and their practical applications to the researchers, field engineers, managers and academicians involved in research, development, academic work and management in hydrology and water resources. This book contains the lecture notes by eminent Isotope Hydrologists of India. The lectures were delivered in a DST-SERC sponsored training workshop under IWIN programme on Isotope Hydrology during December 19-24, 2011. The Course Coordinator was Dr. Bhishm Kumar, Isotope Hydrologist, IAEA and Co-course Coordinator was Dr. R.D. Deshpande, Scientist, PRL, Ahmedabad. This book can be useful to the teaching faculty of various universities and academic institutions for incorporating the isotopes techniques into their PG course curriculum.