One challenge associated with integrating BPM and IoT systems is that the design expertise involved (namely, IoT and BPM) are partitioned across different communities of practice and research. In this chapter, we use the function-behaviour-structure (FBS) framework, a well-established ontology of designing, to bring BPM and IoT perspectives together in a single model. It includes eight fundamental transformations involved in designing business process-driven IoT systems and highlights the interactions between the problem space, which is mainly concerned with the business process domain, and the solution space, which is mainly concerned with the IoT domain. We identify the concept of behaviour as the major connector of the two domains. Representations of behaviour in terms of process models are seen as key boundary objects for the coordination across the different domain experts. We illustrate the notion of behaviour-centred IoT system design by examining an IoT development project carried out as part of a project course at our university.