Petri nets enable a discrete event system of any kind whatsoever to be modeled. They present two interesting characteristics. Firstly they make it possible to model and visualize behaviors comprising concurrency, synchronization and resource sharing. Secondly the theoretical results concerning them are plentiful. The aim of this paper is to present the basic concept relative to Petri nets and the various classes of derived models which can be used for dynamic system modeling. The tool enables qualitative and quantitative analysis and its numerous applications have been still further increased by a number of research workers to enable more condensed descriptions, even where the time factor intervenes, such as synchronized, timed, stochastic, colored and continuous models. Each of these models thus has its own specific character and privileged fields of application. Nevertheless, the ordinary Petri net forms a common basis : it may be likened to a ’common language’ allowing dialogue between persons of very varied training backgrounds.