In most of the world, the term “blood transfusion” usually means the infusion of stored red blood cell (RBC) concentrates, often termed “packed cells”, into the circulatory system. Such transfusions are given in response to severe anemia, significant blood loss, or as therapy (e.g., sickle cell disease). While intended to be beneficial, infusion of stored RBC can impact blood rheology in both large vessels and the levels, but additional factors related to storage are also involved. Thus, understanding the practice and problems of transfusion medicine is a necessary prerequisite for exploring hemorheological changes that occur subsequent to the transfusion of stored cells.