The main aims of the series of volumes "Advances in PetriNets" are:- to present to the "outside" scientific community a fairpicture of recent advances in the area of Petri nets, and- to encourage those interested in the applications and thetheory of concurrent systems to take a closer look at Petrinets and then join the group of researchers working in thisfascinating and challenging area.This volume is based on the proceedings of the 12thInternational Conference on Applications and Theory of PetriNets, held in Gjern, Denmark, in June 1991. It contains 18selected and revised papers covering all aspects of recentPetri net research.