Numerical simulations are in world wide use for the investigation of hydro- and thermodynamic processes in natural waters. In spite of the fact that great achievements have been brought about in this field, numerous questions still remain unanswered, with respect to fundamental formulations as well as to methods of solu- tion. One of the principal objectives of research in our days is the verification of numerical models. The Symposium on Mathematical Modelling in Estuarine PhysiCS was held at Hamburg, Aug. 24 - 26, 1978, with the objective of for- mulating the present standing of research work and of the most im- portant problems in this field. Aspects of physical oceanography and of coastal engineering were to be considered. Estuarine phys- ics were a suitable topic as both disciplines have many points in common there. Eighty-five scientists from sixteen countries convened for two and a half days to discuss details with much interest. We wish to thank them as well as the authors for their contributions. Further, we wish to express our gratitude to the German Research Foundation (Deutsche Forschungsgemeinschaft), Bonn-Bad Godesberg, to the Special Research Project 79 Research in Coastal Waters (Sonder- forschungsbereich 79 Wasserforschung im Klistenbereich ), and to the German Hydrographic Institute (Deutsches Hydrographisches Institut), Hamburg, for sponsoring the meeting and for helping with the organization.