A Study of Atezolizumab in Participants With Locally Advanced or Metastatic Urothelial Bladder Cancer (Cohort 1)

Inclusion Criteria:

* Histologically or cytologically documented locally advanced or metastatic transitional cell carcinoma of the urothelium (including renal pelvis, ureters, urinary bladder, urethra)
* Representative tumor specimens as specified by the protocol
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
* Life expectancy greater than or equal to (\>=) 12 weeks
* Measurable disease, as defined by RECIST v1.1
* Adequate hematologic and end organ function

Cohort 1-Specific Inclusion Criteria

* No prior chemotherapy for inoperable locally advanced or metastatic or recurrent urothelial carcinoma
* Ineligible for cisplatin-based chemotherapy due to one of the following: Impaired renal function, a hearing loss of 25 decibels (dB) at two contiguous frequencies, Grade 2 or greater peripheral neuropathy, or ECOG performance score of 2

Exclusion Criteria:

* Any approved anti-cancer therapy within 3 weeks prior to initiation of study treatment
* Treatment with any other investigational agent or participation in another clinical trial with therapeutic intent within 28 days prior to enrollment
* Active or untreated central nervous system (CNS) metastases as determined by computed tomography (CT) or magnetic resonance imaging (MRI) evaluation during screening and prior radiographic assessments
* Leptomeningeal disease
* Uncontrolled tumor-related pain
* Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures (once monthly or more frequently)
* Uncontrolled hypercalcemia (greater than \[\>\] 1.5 millimoles per liter \[mmol/L\] ionized calcium or Ca \> 12 milligrams per deciliter \[mg/dL\] or corrected serum calcium \> upper limits of normal \[ULN\]) or symptomatic hypercalcemia requiring continued use of bisphosphonate therapy or denosumab
* Malignancies other than urothelial bladder cancer within 5 years prior to Cycle 1, Day 1, with the exception of those with a negligible risk of metastasis or death treated with expected curative outcome or incidental prostate cancer
* Pregnant and lactating women
* History of autoimmune disease
* History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, idiopathic pneumonitis, or evidence of active pneumonitis on screening chest CT scan
* Serum albumin less than (\<) 2.5 grams per deciliter (g/dL)
* Positive test for human immunodeficiency virus (HIV) and/or active hepatitis B or hepatitis C or tuberculosis
* Severe infections within 4 weeks prior to Cycle 1, Day 1
* Significant cardiovascular disease
* Major surgical procedure other than for diagnosis within 28 days prior to Cycle 1, Day 1
* Prior allogeneic stem cell or solid organ transplant
* Administration of a live, attenuated vaccine within 4 weeks before Cycle 1, Day 1
* 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 or render the patient at high risk from treatment complications
* Prior treatment with CD137 agonists or immune checkpoint blockade therapies, including anti-cytotoxic T lymphocyte-associated antigen 4 (anti-CTLA-4), anti-programmed death-1 receptor (anti-PD-1), and anti-programmed death-ligand 1 (anti-PD-L1) therapeutic antibodies