A Study of Atezolizumab Versus Placebo in Combination With Paclitaxel, Carboplatin, and Bevacizumab in Participants With Newly-Diagnosed Stage III or Stage IV Ovarian, Fallopian Tube, or Primary Peritoneal Cancer

Inclusion Criteria:

- Participants receiving a histologic diagnosis of epithelial ovarian cancer (EOC),
peritoneal primary carcinoma, or fallopian tube cancer

- Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2

- Life expectancy greater than (>) 12 weeks

- For participants who receive therapeutic anticoagulation: stable anticoagulant regimen

- Availability of a representative formalin-fixed, paraffin-embedded (FFPE) tumor
specimen in paraffin blocks (preferred) or at least 20 unstained slides (for detailed
tissue requirements at screening)

Exclusion Criteria:

- Received a current diagnosis of borderline epithelial ovarian tumor (formerly tumors
of low malignant potential)

- Have recurrent invasive epithelial ovarian, fallopian tube, or primary peritoneal
cancer that was treated only with surgery (example [e.g.], participants with Stage IA
or Stage IB epithelial ovarian or fallopian tube cancers)

- Have non-epithelial ovarian tumors (e.g., germ cell tumors, sex cord stromal tumors)

- Received prior radiotherapy to any portion of the abdominal cavity or pelvis

- Received prior chemotherapy for any abdominal or pelvic tumor that include neoadjuvant
chemotherapy (NACT) for ovarian, primary peritoneal or fallopian tube cancer

- Received any biological and/or targeted therapy (including but not limited to
vaccines, antibodies, tyrosine kinase inhibitors) or hormonal therapy for management
and/or treatment of epithelial ovarian or peritoneal primary cancer

- Have synchronous primary endometrial cancer

- Have a prior history of primary endometrial cancer, except: Stage IA cancer;
superficial myometrial invasion, without lymphovascular invasion; grade less than (<)
3 or poorly differentiated subtypes, and this includes papillary serous, clear cell or
other International Federation of Gynecological Oncologists (FIGO) Grade 3 lesions

- With the exception of non-melanoma skin cancer and other specific malignancies as
noted above, other invasive malignancies with any evidence of other cancers present
within the last 5 years or previous cancer treatment that contraindicates this
protocol therapy

- Have a known hypersensitivity or allergy to biopharmaceutical agents produced in
Chinese hamster ovary cells or any component of the atezolizumab and/or bevacizumab
formulations

- Undergo major surgical procedure within 28 days prior to first bevacizumab dose, or
anticipation of the need for a major surgical procedure during the course of the study
except participants who receive NACT and will need interval surgery. This may include
but is not limited to laparotomy.

- Have prior allogeneic bone marrow transplantation or solid organ transplant

- Have any other diseases, metabolic dysfunction, physical examination finding, or
clinical laboratory finding giving reasonable suspicion of a disease or condition that
contraindicates the use of an investigational drug or that may affect the
interpretation of the results

- Have any approved or investigational anti-cancer therapy, including chemotherapy or
hormonal therapy, with exceptions: Hormone-replacement therapy or oral contraceptives

- Are administered treatment with any other investigational agent or participation in
another clinical study with anti-cancer therapeutic intent

- Have core biopsy or other minor surgical procedures within 7 days prior to the first
dose of bevacizumab

- Have known sensitivity to any component of bevacizumab

- Have known sensitivity to any component of paclitaxel

- Current treatment with anti-viral therapy for hepatitis B virus (HBV)

- History of leptomeningeal disease