The very ?rst model of concurrent and distributed systems was introduced by C.A. Petri in his seminal Ph.D. thesis in 1964. Petri nets has remained a central model for concurrentsystemsfor40 years,andthey areoften usedasa yardstick for other models of concurrency. As a matter of fact, many other models have been developed since then, and this research area is ?ourishing today. The goal of the 4th Advanced Course on Petri Nets held in Eichsta ¿tt, Germany in September 2003 was to present applications and the theory of Petri Nets in the context of a whole range of other models. We believe that in this way the participants of the course received a broad and in-depth picture of research in concurrent and distributed systems. It is also the goal of this volume to convey this picture. The volume is based on lectures given at the Advanced Course, but in order to provide a balanced p- sentation of the ?eld, some of the lectures are not included, and some material not presented in Eichst¿ att is covered here. In particular, a series of introductory lectures was not included in this volume, as the material they covered is well - tablishedby now,andwellpresentedelsewhere (e.g.,inW. ReisigandG. Roz- berg, eds., ¿Lectures on Petri Nets,¿ LNCS 1491, 1492, Springer-Verlag, 1997 ¿ these two volumes are based on the 3rd Advanced Course on Petri Nets).