This is an observational, non-interventional, medical record review study in CLL patients. A total of 100 patients with CLL who have previously received Arzerra, whether alive or deceased, and have either completed the full course of Arzerra therapy or discontinued treatment early will be eligible to participate in the study. Centers across Europe who are members and non members of the European Research Initiative of CLL (ERIC) and treat CLL patients will participate in the study.