In March 2016 the Dutch Case Studies Project began in which about fifty chaplains participated as co-researchers in collecting practice-based evidence on what chaplains aim for, how they pursue it, and with what results. The chaplain-researchers produced case studies which were discussed collaboratively in research communities which were chaired by academic researchers. The engagement of chaplains in research can be understood from the development in the profession of integrating research into chaplaincy. While it is presumed that research benefits chaplains’ practices, so far the impact of research on chaplains’ practice had not been studied. Based on mixed-methods (observation, interviews, survey, focus groups), this dissertation describes, analyzes and reflects on the perceived change of chaplains’ professionalism as a result of their participation in the Case Studies Project. This practical theological research provides insight in the value of the double role of chaplain-researcher for chaplains’ professionalism. Niels den Toom (1988) studied theology at Leiden University and the Protestant Theological University and has worked as a chaplain. He wrote his dissertation at the Protestant Theological University.