The World Health Organization established World Blood Donor Day in 2004, before it was formally adopted by the World Health Assembly in 2005 during its 58th session, becoming an annual global health day observed on June 14. The date honors the birthday of Austrian scientist Karl Landsteiner, the Nobel laureate who discovered blood groups and their classification system. The day thanks unpaid voluntary blood donors who save millions of lives each year and raises awareness of the ongoing need for safe, adequate blood supplies to support emergency care, surgeries, and treatment of chronic conditions such as cancer and hereditary anemias. It emphasizes that regular, voluntary donation is the best safeguard for a safe blood supply, compared to paid donation, which can increase the risk of disease transmission. Health ministries, blood banks, and civil society organizations worldwide mark the occasion with blood donation drives, events honoring regular donors, and awareness campaigns encouraging more healthy individuals to donate regularly to ensure stable medical supplies.