Perinatal hemolytic disease is characterized by the destruction of fetal red blood cells by maternal antibodies directed against membrane antigens and can lead to immune fetal hydrops. More than 250 blood group antigens have been described. After considering the particular situation of ABO incompatibility, this article describes the classification of red blood cells antigens, with particular reference to the Rhesus system. Other antigens such as Kell, Kidd, Duffy, MNSs, P and Lutheran are also considered.