This is an open-label, multicenter, randomized, Phase III study to investigate the efficacy and safety of venetoclax in combination with rituximab (venetoclax+R) compared with bendamustine in combination with rituximab (BR) in participants with relapsed or refractory chronic lymphocytic leukemia (CLL). Participants will be randomly assigned in 1:1 to receive either venetoclax+R (Arm A) or BR (Arm B).