The main idea behind the series of volumes Advances in PetriNets is to present to the general computer science communityrecent results which are the most representative andsignificant for the development of the area. Thepapers forthe volumes are drawn mainly from the annual InternationalConferences on Applications and Theory of Petri Nets. Selected papers from the latest conference are independentlyrefereed, and revised and extended as necessary. Somefurther papers submitted directly to the editor areincluded. Advances in Petri Nets 1991 covers the 11th InternationalConference on Applications and Theory of Petri Nets held inParis, France in June 1991. The volume contains theBibliography of Petri Nets 1990 prepared by H. Plnnecke andW. Reisig, with over 4000 entries.