Since the early 80s the use of blood products in treating critically ill animals and supporting animals undergoing surgical and other procedures has tremendously increased. However, it should be noted that blood products are prepared from donor animals and represent a very limited resource not available in all situations, and as they are biologicals they bear the inherent risks to transmit infectious agents and cause other adverse transfusion reactions. Furthermore, the need for blood typing and crossmatching of patients and donors has now been recognized in order to assure safe and more efficacious transfusions in dogs and cats. Veterinary clinicians play a key role in providing safe and effective transfusion therapy.