The HARMONY Patient Cluster is a unique group of 9 European Patient Umbrella Organizations working in the different areas of hematological diseases within the HARMONY Alliance. The 9 Patient Organizations combine years of expertise in patient-led scientific research and policy advocacy, and use this experience to the benefit of the affected patient communities. The Patient Cluster and their patient communities are consistently involved in the definition of outcomes, the design of Research Projects and the information of patients. In addition the Patient Cluster also make sure that there is a reliable bi-directional flow of information within and outside of the Alliance. For the first time in a major research project, the patient community sits at the table as truly equal partners to researchers, industry and regulators. The HARMONY Patient Cluster experience will also be captured and promoted in publications and on social media.