The Kell System is a blood group system that includes a variety of antigens found on the surface of red blood cells. It is important in blood transfusions and pregnancy, as incompatibility can lead to serious health issues. The most significant antigens in this system are K and k, which can trigger immune responses in individuals who lack them. Discovered in the 1940s, the Kell System is one of the many blood group systems used to classify human blood. Testing for these antigens is crucial for ensuring safe blood transfusions and managing conditions like hemolytic disease of the newborn, where maternal antibodies attack fetal red blood cells.