Hematology is a branch of medicine that concerns itself with the study of blood, the blood-forming tissues, and its diseases. The word "heme" comes from the Greek for blood and the physicians working in this field are called hematologists. Initially, hematologists complete a four-year medical degree which is followed by 3 or 4 years in an internship or residency program. Thereafter, they spend 2 or 3 more years of learning how to diagnose and treat blood disorders.