Alloimmunization to non-ABO antigens is one of the most common complications of blood transfusions. Blood group antigen profiling and prophylactic antigen matching have reduced but not eliminated alloimmunization. DNA-based genotyping methods enable accurate prediction of most blood group antigen phenotypes. Compared to traditional serologic typing, genotyping is particularly useful for patients with recent transfusion or to identify low frequency antigens for which serologic reagents are not available. Genotyping can also identify variant RH alleles that are common in patients with sickle cell disease, allowing more precise matching between patients and blood donors. In this session, we will review the challenges for blood group antigen genotyping focusing on Rh antigens, and discuss strategies to incorporate genotyping results to improve red cell matching and prevent alloimmunization.