Protecting groundwater resources from pollution has been a high-priority topic in recent years. A variety of processes, and soil and aquifer properties, affect aquifer vulnerability. The determination of the parameters characterizing these processes is essential for modelling and predicting the migration of pollutants in groundwater systems. Major objectives are to prevent pollution and degradation of groundwater resources, or, if contamination has already occurred, to identify its origin so that remedies can be proposed. At the IAEA, emphasis has been placed on practical applications of nuclear and isotope techniques that are directly or indirectly related to the solution of groundwater pollution problems. This article reports on how some of these techniques have been used in practice. Isotope tracer techniques have some problems and limitations, however. As a result, in the area of pollution migration studies, scientific emphasis is now shifting from the development and improvement of particular isotope tracer techniques to their complex utilization in combination with traditional methods. This is happening in order to provide the information that is needed to make relevant prognoses and propose countermeasures. 5 figs