In several mental health organisations in the Netherlands users’lived experiences are seen as a source of knowledge: experiential knowledge, that can be used professionally.  As a 'third source of knowledge', it is seen as a necessary equivalent source to that of scientific and professional knowledge. Our research team has seven years of experience in action research implementing experiential knowledge in five mental health organisations.  Experiential knowledge has six characteristics, summarised in the acronym PEPPER. Experiential knowledge is Practical, Existential, Political-Critical, Personal, Ethical and Relational. In the presentation, we give practical and artistic examples of these six characteristics. We describe what happens when experiential knowledge is implemented as a source of knowledge in mental health organisations.  Experiential knowledge is also potentially present among nurses, social workers, psychologists and psychiatrists. To learn how to use experiential knowledge properly, they can take training courses. The first master Experiential Knowledge started September 2023 at Windesheim University of Applied Sciences. When experiential knowledge is given space, interesting dynamics take place between clients, professionals and management.  It contributes to a more equal and reciprocal contact between clients and professionals. It promotes recovery-oriented work and reduces the stigma attached to psychiatric disorders and addiction. To give experiential knowledge real space, a number of conditions are needed. In our presentation, we will discuss some dilemmas and questions we encountered in our action research. At the moment there are about 400 educated professionals-with-experiential expertise working in the mental health sector in the Netherlands and about 1000  educated professional peer support workers. The dutch Association of Experiential Experts (VvED)  promotes the professionalisation of experiential experts. The presentation will be given by professor dr. Alie Weerman, three researchers from her research group and by the president of the Dutch Association of Experiential Experts.