This chapter discusses getting introduced to blood, which has been one of the most attractive parts of the body. Blood is a complex fluid, only about half of which is actually a fluid and other half consists of cellular elements. The portion of blood which is in exchange with the interstitial fluid is changing continuously. Blood is a brilliant evolutionary invention which has made possible large multicellular organisms and terrestrial existence. Developments in cellular and molecular biology have given a new insight into the functions of various elements of blood in health and disease, thereby making possible new approaches to treatment of derangements such as coagulation disorders and leukemias. New blood is ultimately derived from food, but the heart has no role in the transformation. Both arteries and veins carry blood but the arterial blood has more oxygen, which is actually obtained from the air.