Blood groups are classified into several subsystems according to the antigen determinants distributed on surface of red blood corpuscles. The genetic map of blood group is located on several chromosomes of human genome. The study of blood groups is very important in medical use, especially blood transfusion, paternity test and forensic medicine. This book highlights on the using of molecular techniques such as polymerase chain reaction (PCR) and restriction fragment length polymorphisms (RFLP) in the detection of the genotypes of ABO blood group in Iraqi population. The using of these techniques are so important in determining the blood group from DNA samples ( such as sperm, saliva, hair, nail, and blood stain) extracted from crime scene. This book reviewed the recent references concerned with this subject worldwide.