The transition towards a circular economy puts pressure on the purchasers to purchase in a circular manner. However there are many hurdles to overcome. The aim of this research is to investigate the role of the purchasers in the circular purchasing process and investigate the drivers and constraints that influence circular purchasing. We interviewed purchasers, supervisors and policymakers of successful and unsuccessful organizations and organizations that showed the intention towards transitioning towards circular purchasing by signing a green deal and organizations that did not show this intention. The results of this comparative case study show that the main role of the purchaser is that of coordinator, facilitator and advisor, but the combination of being intrapreneurial, sustainability minded and having knowledge about the circular economy describe the circular purchaser. The drivers (creating sense of direction and grasping the complexity of the circular economy) that influence circular purchasing are identified. Also, the market, organizational, law related, concept related and culture related constraints are identified. In general the circular purchasing process differs from a regular process in the level of freedom offered to suppliers during the request phase."