Process models are the basis for a wide range of critical activities within an organisation. It is not surprising then that process models, and the act of process modelling, have been the focus of much research over the last two decades. Recent research indicates, however, that common process modelling notations lack sufficient representation for capturing business rules. Although the need for business processes and business rules to be modelled in an integrated manner is well established, the body of knowledge on integrated modelling of the two is limited. In this paper our aim is to review the state of related research and develop a research agenda, based on a systematic review of related literature, to advance research in this field. We present a consolidated view of the benefits of rule and process model integration, together with an overview of current related approaches, and a research agenda going forward.