World Marrow Donor Day is observed worldwide every third Saturday of September to celebrate hematopoietic stem cell donors and highlight the importance of bone marrow transplants in saving lives. The day was initiated by the World Marrow Donor Association (WMDA), which maintains the largest bone marrow donor database, comprising nearly 38 million donors from over 50 countries as of 2020. The history of bone marrow transplantation dates back to the mid-20th century, with significant milestones including the first successful allogenic transplant by Georges Mathé in 1958 and the first non-twin transplant by Robert A. Good in 1968. The observance aims to encourage the creation and maintenance of donor registries, as finding a compatible donor is crucial for successful transplants. Activities on this day often focus on educating the public, healthcare professionals, and government officials about the significance of bone marrow donation.