The word “apheresis” is derived from the ancient Greek word for “separation.” Apheresis is a therapeutic process in which blood is drawn from the body, pathogenic substances are removed from the blood, and the blood is returned to the body. The scope of apheresis is outlined in Table 1.1. Many diseases are potential targets for treatment with apheresis. The diseases that can be reimbursed for apheresis therapy by the Japanese government are listed in the last section of this book. These diseases include autoimmune disease, kidney disease, liver disease, gastrointestinal tract disorders, and hematologic disorders.