The contents of the book are assembled from selected papers presented during the International Conference on Isotopes in Environmental Studies – AQUATIC FORUM 2004 convened in Monaco from 25 to 29 October 2004, which was the most important gathering of the year of isotope environmental scientists. The book reviews the present state of the art isotopic methods for better understanding of key processes in the aquatic environment, responsible for its future development and its protection. The main highlights include the latest developments in the study of the behaviour, transport and distribution of isotopes in the aquatic environment, recent climate change records using isotopic tracers in the environment, global isotopic oceanic studies, new trends in radioecological investigations and modelling, impact of groundwater-seawater interactions on coastal zones, groundwater dynamics and modelling, important for management of freshwater resources, development of new isotopic techniques, such as AMS, RIMS and ICPMS, and their applications in environmental studies, new trends in radiometrics underground techniques, new in situ radiometrics technologies and many other exciting topics which were presented and discussed during the Conference. The proceedings constitute an important contribution to the environmental isotopic research. In publishing this book the aim is to make the use of isotopes more widespread in the environmental disciplines and to further stimulate work in this exciting field.