Chronic lymphocytic leukemia (CLL) is the most common leukemia (cancer of blood cells). The purpose of this study is to assess the safety of venetoclax in combination with obinutuzumab or acalabrutinib in the treatment of CLL. Adverse events and change in disease activity will be assessed. Venetoclax in combination with obinutuzumab or acalabrutinib is being investigated in the treatment of CLL. Study doctors put the participants in 1 of 4 groups, called treatment arms. Participants will receive oral venetoclax in combination with intravenously (IV) infused obinutuzumab or oral acalabrutinib at in different dosing schemes as part of treatment. Approximately 120 adult participants with CLL who are being treated with venetoclax will be enrolled in the study in approximately 80 sites worldwide. Participants in Arm A will receive oral venetoclax in combination with IV infused obinutuzumab, with a 5 week venetoclax ramp up. Participants in Arm B will receive oral venetoclax in combination with oral acalabrutinib, with a 5 week venetoclax ramp up. Participants in Arm C and Arm D will receive oral venetoclax in combination with oral acalabrutinib, with differing venetoclax ramp up periods. The total study duration is approximately 28 months. There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.