Hematology is defined as the study of normal and pathologic aspects of blood and blood cells. Hematopoiesis (hemopoiesis) is the continuous, regulated process of blood cell production, or formation. Hematopoietic (hemopoietic) system consists of all organs and tissues involved in hematopoiesis, and these are divided into myeloid tissue and lymphoid tissue. The hematopoietic stem cell (HSC) is the progenitor of all the cells in blood and gives rise to cells of both myeloid and lymphoid system. Disorders of red cells, anemia, iron deficiency anemia, megaloblastic anemia, pernicious anemia, anemias of blood loss, aplastic anemia, hemolytic anemia, hereditary hemolytic anemia, beta-thalassemia major, sickle cell anemia, acquired hemolytic anemias, disorders of white cells, normal differential leukocyte count, quantitative disorders of leukocytes, acute leukemia, acute lymphoblastic leukemia/lymphoma, acute myelogenous leukemia, chronic myelogenous leukemia, chronic lymphocytic leukemia, disorders of hemostasis, normal hemostasis, classification of hemostatic disorders, immune thrombocytopenic purpura, coagulation disorders, etc. are discussed in this chapter. 11 well-illustrated tables, 16 well-labeled figures, and 27 well-illustrated boxes are also presented in this chapter.