Welcome to Aachen and to the First European Simulation Congress ESC83, a triennial international conference jointly promoted by ASIM/GI, DBSS, SIMS and UKSC. ESC83 is organized by ASIM/GI,. supported by SCS and IMACS, and sponsored by NGI (section for simulation). It takes place at the Karman Auditorium of the Aachen Technical University, FRG. The aim of ESC83 is to cover all aspects of modeling and simulation in theory and practice, to promote the exchange of knowlewdge and experience between different international research groups in this field, and to strengthen the international contact between developers and users of modeling and simulation techniques. On the occasion of the Congress people of scientific and engineering disciplines will meet to discuss the state of the art and future activities and developments. A large number of contributed papers has been strictly examined and selected by the Scientific Committee to guarantee a high international standard. The book contains the accepted papers that will be presented at the Congress. The papers have been classified according to the following keywords.