The investigation of blood groups of animals is of eminent importance not only for clinical and forensic veterinary medicine and animal breeding but also for comparative medicine, experimental surgery including transplantation and particularly xeno-transplantation. Animal blood groups play an important role in basic sciences such as immunobiology and immunogenetics. Blood group research is closely connected with the development of immunology and immunochemistry and has added new and decisive impulses to the field of genetics. Research on blood groups shares methods with immunology, serology and genetic and thus opens a whole variety of genetically controlled characteristics of the animal kingdom. Blood groups afford as markers for the smallest genetical units an insight in molecular biology and the dynamic of genetic. The exploration of serology and genetic of cellular and soluble blood groups on eryth-rocytes, leukocytes, and thrombocytes in serum and other body fluids of animals has reached a remarkable standard. Newest results concerning investigations on lym-phocyte antigens, serogenetics, immuno-regulation and tumour-immunology show that this field is not yet completed. In contrast, in many areas research is just starting to understand. In a time of rapid development of immuno-genetics we complied a monography on blood groups of animals. After more than 30 years of fascinating own work about blood groups of animals it is the aim, not only to provide safe results but also to show problems and limits of this research and in addition to stimulate new research. The literature which covers this field is immense. We therefore were forced to select the most important publications.