ABO incompatible kidney transplantation is indicated for patients for whom no ABO-identical or minor mismatch donor is available. Since the author and his colleagues performed the first ABO-incompatible kidney transplantation in Japan in 1989, 400 such transplantations have been performed in 41 hospitals in Japan and this practice has contributed to a number of new developments. One is a clearer and more suitable model for conceptualising the mechanism of humoral immune response which enables identification of antigens and antibodies and a therapeutic strategy against rejection. The rejection mechanisms are discussed not only from the perspective of immunology but also viewed from different angles, including anatomy, microscopic and macroscopic pathology, molecular biology and haematology. Immunosuppressive therapy is discussed, divided in four categories: extracorporeal immunomodulation with removal of humoral antibodies; drug therapy to suppress cellular immunity; splenectomy; and anticoagulation therapy. Surgical procedures for kidney transplantation and splenectomy are treated, including discussion of the best timing for the latter. The book gives an overview of the current status with statistics and results of questionnaires and ends with discussions of 17 case histories.