This volume contains the proceedings of the 21st International Conference on Application and Theory of Petri Nets. The aim of the Petri net conferences is to createaforumfordiscussingprogressintheapplicationandtheoryofPetrinets. Typically, the conferenceshave 100{150participants{ one third of these coming from industry while the rest are from universities and research institutions. The conferences always take place in the last week of June. The conference and a number of other activities are co-ordinated by a ste- ingcommittee withthe followingmembers:G.Balbo(Italy),J.Billlington(A- tralia),G.De Michelis(Italy),C.Girault(France),K.Jensen(Denmark),S.- magai (Japan), T. Murata (USA), C. A. Petri (Germany; honorary member), W. Reisig (Germany), G. Roucairol (France), G. Rozenberg (The Netherlands; chairman), and M. Silva (Spain). Otheractivitiesbeforeandduringthe2000conferenceincludedtoolpresen- tions and demonstrations, a meeting on Interchange Formats", extensive int- ductorytutorials,twoadvancedtutorialsonHardwareDesign"andTimedand Hybrid Automata", and two workshops on Software Engineering" and Pr- tical Use of High-Level Nets". The tutorial notes and workshop proceedings are not published in these proceedings, but copies are available from the organisers. The 2000 conference was organised by the CPN Group at the University of Aarhus, Denmark. We would like to thank the organisers (see next page) and their teams. WewouldliketothankverymuchallthosewhosubmittedpaperstothePetri net conference.We receiveda totalof 57submissions from 20di erent countries. This volume comprises the papers that were accepted for presentation. Invited lectures were given by Jordi Cortadella, Philippe Darondeau, Gregor Engels, Serge Haddad, Kim Guldstrand Larsen, and Ole Lehrmann Madsen.
