Blood type compatibility is crucial for safe blood transfusions and organ transplants. There are four main blood types: A, B, AB, and O, each of which can be either Rh-positive or Rh-negative. Compatibility is determined by the presence or absence of specific antigens on the surface of red blood cells. For example, a person with type A blood can receive blood from type A or type O donors. In general, type O is considered the universal donor, as it can be given to any blood type. Conversely, type AB is the universal recipient, meaning individuals with this blood type can receive blood from all other types. Understanding these compatibilities helps prevent serious reactions during medical procedures.