Blood transfusion is the process of transferring blood into the vein of a patient. It is a therapeutic treatment used to restore blood or plasma volume after substantial bleeding, burns or trauma. Transfusion increases the quantity and concentration of red blood cells in anemic patients for improving the oxygen-carrying potential of the patient's blood. Transfusions are also used frequently as an important adjunct in various surgical operations where patients lose considerable volumes of whole blood that must be restored. Some of the important advancements in transfusion therapy include blood typing, pathogen screening and blood substitutes. Blood typing is a method of classifying blood in accordance with the distinctive inherited characteristics, related to the presence and absence of antibodies and antigens located on the surface of erythrocytes. There are various blood groups found in humans including ABO, Rh, Kidd, Kell, Duffy, MNS and Lewis group. The receiver and donor must have the same or compatible blood types. Therefore, identification of these variables has become critical in the context of blood transfusion. This book strives to provide a fair idea about blood transfusion and help develop a better understanding of the latest advances within this area. Its extensive content provides the readers with a thorough understanding of the subject.