Blood transfusion involves administering one of the components of blood (red blood cells, platelets, granulocytes, plasma)—obtained from healthy individuals known as "donors"—to sick individuals known as "recipients." Each year in France, approximately 600,000 patients are treated with blood products derived from 1.6 million volunteer blood donors. The safety of blood products relies on two essential steps: donor recruitment and screening prior to donation, followed by the biological qualification of the donation. The first step aims to exclude from donation individuals exhibiting symptoms or risk factors for blood-borne diseases. The second step ensures that a potentially harmful blood product is excluded from any therapeutic use, that the donor is permanently or temporarily excluded, and, in the event of a biologically confirmed infection, that the donor is informed so they can access appropriate therapeutic care and medical counseling. Finally, to further reduce the risk of transmitting infections, particularly viral ones, other measures such as leukocyte removal or viral inactivation of plasma have been implemented over the past 20 years.