The Picture Exchange Communication System (PECS) is a protocol designed to teach functional communication skills to individuals with developmental disorders. It is based on the Applied Behaviour Analysis approach (ABA). There are many studies proving the effectiveness of the PECS method in developing communication skills. However, in order to fully evaluate the effectiveness of a therapeutic approach, it is important to assess the potential generalization of its outcomes to other settings and the maintenance of treatment effects. In this paper, we have reviewed the studies in which transfer of skills to other settings and the maintenance of effects over time were analysed. We have also discussed their implications for practitioners who use the PECS method.