Red blood cells (RBCs), the most abundant cells in the human body and essential to life, possess unique properties. Erythropoiesis, the process of red blood cell formation, is a fascinating system that produces two million cells per second. Studying abnormalities in this system leads to significant advances in fundamental science, pathophysiology, and therapeutic approaches—not only for hemoglobinopathies but also across a broad range of scientific and medical disciplines. Red blood cells represent a major societal issue due to the medical and social consequences of red blood cell disorders, blood doping in France and worldwide, and the challenges surrounding blood transfusion. Leveraging innovative tools, GR-Ex brings together researchers and physicians from all disciplines within our university to advance knowledge, education, and care at both national and international levels.