Blood groups are inherited. Most familiar are the blood types of the A-B-O group and Rh types, but several others have been found that display the antigen-antibody reaction.

In the seventeenth century, the idea of saving lives by transfusion was first proposed. Many of these early attempts resulted in death until German-born immunologist Karl Landsteiner (1864-1943) found that mixing blood from different individuals would, in some cases, cause the mixed cells to form a clump. This clumping of cells was responsible for the deaths of many of the early transfusion patients. Landsteiner concluded that substances on the surface of the red cells were responsible for the clumping reaction, these proteins were called these antigen A and B. Blood cells without these antigens were placed into the O group (pronounced as the letter "O"). Landsteiner also found a type AB type cell that has both...