Transfusion medicine is the branch of medicine that is concerned with the process of collecting (donation), testing, processing, storing, and transfusing blood and its components. It is a cornerstone of emergency and surgical medicine. The blood collection process typically takes place in donor centers. Blood banks are sections of clinical laboratories that process, test, and distribute blood and its components.

AABB (formerly American Association of Blood Banks) estimates that 9.2 million volunteers donate blood each year. About 15.7 million units of whole blood and red blood cells were donated in the United States in 2011. An average of 30 million units of blood components are transfused annually in this country. Blood transfusions, the introduction of blood or blood components from one person into the bloodstream of another, are essential for saving the lives of victims of trauma, for those undergoing major surgery, and for those with other causes of blood loss. Blood transfusions also are used to treat severe anemia resulting from the effects of chemotherapy, cancer, sickle cell disease, and thalassemia, to name a few examples.

Organizations such as AABB and blood donor center systems such as the American Red Cross and America's Blood Centers give a great deal of attention to both the safety and the maintenance of the nation's blood supply. In particular, they monitor potential problems with the supply, such as reduced numbers of blood donors and the risk of transmittal of blood-borne infections.