Process algebras are formalisms that describe the concurrent behaviour of systems. In recent years, they have been applied to the modelling of biological systems. Bio-PEPA is a quantitative process algebra used for this type of modelling and it is based on the stochastic process algebra PEPA which was developed for modelling the performance of human-created systems such as computer networks. In this presentation, the syntax and semantics of Bio-PEPA will be introduced, as well as the different analysis techniques that are available for Bio-PEPA models. A model of protein trafficking within the mammalian cell and related results will be described, and if time permits, semantic equivalences for Bio-PEPA will be briefly discussed. This is joint work with Jane Hillston.