The most common blood type among humans is O positive. Blood types are determined by the presence or absence of specific antigens on the surface of red blood cells, with the ABO and Rh factor systems being the most significant. Approximately 37% of the global population has O positive blood, making it a crucial type for blood donations, as it can be given to any positive blood type recipient. Understanding blood types is vital for medical procedures, including transfusions and organ transplants, ensuring compatibility and reducing the risk of adverse reactions.