Blood typing is a system used in hematology to classify blood based on the presence or absence of specific antigens on the surface of red blood cells. The most widely recognized classification systems, such as the ABO system, categorize blood into types that determine the compatibility of blood products for transfusion. Compatibility is critical because mixing incompatible blood types can trigger severe immune responses involving agglutination, where the foreign antigens cause the recipient's plasma to clump the donated cells. Further systems, including the determination of the Rh factor, assess the presence of additional proteins that influence physiological compatibility, making accurate blood typing essential for safe medical procedures and blood banking.