This book presents recent and important research on Chronic lymphocytic leukemia (or "chronic lymphoid leukemia"), known for short as CLL, which is a type of leukemia in which too many lymphocytes are produced. Although the malignant lymphocytes in CLL may look normal and mature, they are not and these cells may not cope effectively with infection. CLL is the most common form of leukemia in adults. Men are twice as likely to develop CLL as women. However, the key risk factor is age; over 75% of new cases are diagnosed in patients over age 50.