The aim of this paper is the introduction of preemption in a compositional model, called M-nets, which is based on Petri nets and hence provided with a concurrent semantics. We propose a way to model preemptible systems by extending the M-net model with priorities and the M-net algebra with a preemption operator. We show that these extensions can be seen as a high-level version of the well studied model of priority systems, and so, can be reduced to Petri nets (without priori- ties) which retain as much as possible of the original concurrency. As a consequence, Petri nets appear as a model powerful enough to deal with preemption in a compositional way and with a concurrent semantics.