Non-Hodgkin's lymphoma (NHL) is a cancer that arises from the transformation of normal B and T lymphocytes (white blood cells). The purpose of this study is to assess the safety, pharmacokinetics, and preliminary efficacy of ABBV-101 in adult participants in relapsed or refractory (R/R) non-Hodgkin's lymphomas: chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), diffuse large b-cell lymphoma (DLBCL), non-germinal center B cell (GCB) DLBCL, mantle cell lymphoma (MCL), follicular lymphoma (FL), marginal zone lymphoma (MZL), Waldenström macroglobulinemia (WM), or transformed indolent NHL. Adverse events will be assessed.

ABBV-101 is an investigational drug being developed for the treatment of NHL. This study will include a dose escalation phase to determine the maximum administered dose (MAD)/Maximum tolerated dose (MTD) of ABBV-101. Dose expansion part 2A will follow to further determine the safety and change in disease activity in participants with first line treatment (1L\[non-US only\]), second line or later of treatment (2L)+ CLL/SLL or third line or later of treatment (3L+) non-GCB DLBCL receiving ABBV-101 alone. Dose expansion Part 2B (non-US only) will follow to determine the safety and change in disease activity in participants with 1L or 2L+ CLL/SLL receiving ABBV-101 in combination with oral venetoclax. Approximately 390 adult participants with multiple NHL subtypes will be enrolled in the study in sites world wide.

In the dose escalation phase of the study participants will receive escalating oral doses of ABBV-101, until the MAD/MTD is determined, as part of the approximately 100 month study duration. In the dose expansion phase of the study participants receive oral ABBV-101 alone or oral ABBV-101 at a dose determined in the dose escalation phase in combination with oral venetoclax, as part of the approximately 100 month study duration.

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 an approved institution (hospital or clinic). The effect of the treatment will be frequently checked by medical assessments, blood tests, and side effects.