On February 4, 1937, a hospital-based facility widely recognized as the first practical, continuously operating blood bank opened and began systematic collection, processing, storage, and distribution of donor blood for clinical transfusion. This development built on decades of research into blood groups, anticoagulants, refrigeration, and crossmatching, and represented the transition from ad hoc, bedside direct transfusions to an organized supply that could serve multiple patients on demand. Background: Throughout the late 19th and early 20th centuries, clinicians and scientists advanced knowledge critical to transfusion safety and logistics. Karl Landsteiner’s discovery of the ABO blood groups in 1901 established why some transfusions caused fatal reactions; subsequent work identified additional blood-group systems and refined compatibility testing. The introduction of anticoagulants (most importantly sodium citrate) and improved refrigeration made it feasible to store blood for short periods. Still, early transfusions were typically performed directly from donor to recipient or relied on limited, short-term storage. What changed in 1937: The new blood bank implemented routine procedures for recruiting and screening donors, collecting blood into anticoagulant solution, separating or storing whole blood under controlled refrigeration, and performing pretransfusion crossmatching. That operational model allowed hospitals to keep a ready inventory of compatible blood types, reducing delays in emergencies and elective surgery and improving survival in cases of severe hemorrhage. Impact: The establishment of a reliable blood bank altered clinical practice. Surgeons could plan operations with greater assurance of available blood; emergency services could respond faster to trauma and obstetric hemorrhage; and public health systems could envision broader collection efforts. The concept spread rapidly, with other hospitals and municipal services adopting similar organizational and technical standards in subsequent years. During the late 1930s and especially in World War II, blood-banking techniques were further scaled and standardized to meet military and civilian needs. Limitations and context: Claims about the “first” blood bank can vary depending on criteria—such as whether one emphasizes continuous operation, scale, clinical impact, or formal institutional recognition. Earlier experiments and short-term storage efforts occurred in several countries, and some institutions performed pioneering collections and transfusions before 1937. Historians typically identify the 1937 facility as the first to combine routine donor recruitment, standardized collection and anticoagulation, refrigerated storage, and systematic crossmatching to supply multiple patients reliably over time. Legacy: The operational model introduced then remains the foundation for modern transfusion services: organized donor programs, laboratory-based compatibility testing, regulated storage and distribution, and transfusion oversight. Over subsequent decades, advances such as fractionation, blood-component therapy, viral screening, and computerized inventory management further transformed the field, but the 1937 blood bank stands as a pivotal step from experimental transfusion toward a dependable public-health resource. Sources and verification: This summary is based on established histories of transfusion medicine that trace the incremental technical and organizational advances leading to hospital-based blood-banking in the 1930s. Precise attributions and competing claims are discussed in specialist historical literature; when exact institutional firsts are asserted, historians note differences in definitions and criteria.