Tracing techniques have reached an increasing importance in hydrology and hydrogeology. New fields of application arise and new methods were developed in order to meet the recent requirements. Tracers have been used for several decades to study flow conditions, for groundwater reconnaissance and for management of water resources. Due to strong pollution of the environment water protection is one of the main issues, The application of artificial and natural tracers can help in various ways to assess and to predict contaminant transport in surface water as well as in the unsaturated and saturated zone of the underground. The proceedings contain papers on: New methodical developments in tracing techniques; Application of tracers in the various fields of hydrological studies including environmental problems; Use of tracer experiments the improvement and validation of mathematical models.