Chronic lymphocytic leukaemia (or chronic lymphoid leukaemia ), known for short as CLL, is a type of leukaemia 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 leukaemia 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. This book presents important research from around the world in this field.