Abstract
Nested Petri nets (NP-nets) is a Petri net extension, allowing tokens in a net marking to be represented by marked nets themselves. The paper discusses applicability of NP-nets for modeling task planning systems, multi-agent systems and recursive-parallel systems. A comparison of NP-nets with some other formalisms, such as OPNs of R. Valk, recursive parallel programs of O. Kushnarenko and Ph. Schnoebelen and process algebras is given. Some aspects of decidability for object-oriented Petri net extensions are also discussed.