Chronic lymphocytic leukemia (CLL), a form of Non-Hodgkin's Lymphoma, is the most common type of leukemia in adults, affecting approximately 3,800 people in the UK each year. This study will evaluate the patient experience of CLL in adult participants who are prescribed venetoclax+rituximab or Bruton's tyrosine kinase inhibitors in the United Kingdom (UK).

Venetoclax+rituximab is a drug approved to treat CLL. Study participants will receive venetoclax+rituximab as prescribed by their study doctor in accordance with approved local label. Adult participants prescribed venetoclax+rituximab or Bruton's tyrosine kinase inhibitors will be enrolled. Around 140 participants will be enrolled in the study in approximately 10 sites in the UK.

Participants will receive venetoclax tablets to be taken by mouth and rituximab intravenous (IV) injection according to the approved local label.

There is expected to be no additional burden for participants in this trial. All study visits will occur during routine clinical practice.

Inclusion Criteria:

• Has a confirmed diagnosis of chronic lymphocytic leukemia (CLL) (as defined by 2008 Modified International Workshop for Chronic Lymphocytic Leukemia National Cancer Institute Working Group (IWCLL NCI-WG) Guidelines).
• Has relapsed/refractory (R/R) disease having received only 1 prior line of treatment, which must have been a chemotherapy or chemoimmunotherapy treatment.
• Has treatment experience with venetoclax+rituximab (Ven+R) or bruton's tyrosine kinase inhibitor (BTKi)s that meets the criteria for inclusion described in the protocol, for which recruitment targets have not yet been met.

Exclusion Criteria:

• Previously treated with a BTKi, a BCL-2 inhibitor or other investigational agents.
• Has any other medical condition or disorder that, in the opinion of the site investigator or study director, could compromise participant's ability to give written informed consent and/or prevent or interfere with his or her ability to comply with study procedures and provide meaningful information about his or her CLL experience.

Adult participants with second-line (2L) chronic lymphocytic leukemia (CLL) treated with venetoclax+rituximab or bruton's tyrosine kinase inhibitors per approved local label in the United Kingdom.