Background: Paclitaxel or pegylated liposomal doxorubicin in combination with bevacizumab constitutes a standard treatment option in patients with relapsed ovarian cancer who are not considered candidate for platinum, but responses are short-lived. Immune checkpoint inhibitors like atezolizumab as single agents have limited activity in ovarian cancer. There is a biologic rationale to combine checkpoint inhibitors with chemotherapy and bevacizumab, however, the role of such combination for the management of ovarian cancer is so far undefined. Because of the intimate relationship between angiogenesis and immunosuppression, it is expected that the inhibition of both pathways could lead to synergism and more durable clinical benefit. The addition of a chemotherapeutic agent is expected to lead to the release of tumor antigens and enhance the efficacy of immunotherapy in turn. Therefore, we aim to test the efficacy of atezolizumab in combination with non-platinum-based chemotherapy and bevacizumab vs the combination of a non-platinum-based chemotherapy and bevacizumab alone. Methods: AGO-OVAR 2.29 is a randomized (1:1), double blinded, phase III trial evaluating the efficacy and safety of atezolizumab plus bevacizumab and chemotherapy (weekly paclitaxel or pegylated liposomal doxorubicin) compared with placebo plus bevacizumab and chemotherapy in patients with recurrent ovarian, fallopian tube, or primary peritoneal cancer with 1st or 2nd relapse within 6 months after completing platinum-based chemotherapy or 3rd relapse. A de novo tumor biopsy to determine the PD-L1 expression status prior to randomization for stratification is mandatory. Patients are treated with chemotherapy plus bevacizumab + atezolizumab/placebo until progression or unacceptable toxicity. Co-primary endpoints are overall survival and progression-free survival. It is planned to randomize approximately 664 patients. Safety interim analyses were performed after inclusion of 24 and an additional 60 and 120 patients who had completed at least one treatment cycle. As of 09^th February 2022, 461 patients have been randomized. Clinical trial information: NCT03353831.