This is a multicenter Phase 1b, open-label study to assess safety, tolerability, preliminary efficacy, and pharmacokinetics (PK) of cabozantinib taken in combination with atezolizumab in subjects with advanced urothelial carcinoma (UC) (including bladder, renal pelvis, ureter, urethra) or renal cell carcinoma (RCC). The study consists of two stages: in the Dose Escalation Stage, an appropriate recommended cabozantinib dose for the combination with standard dosing regimen of atezolizumab will be established. In the Expansion Stage, tumor-specific cohorts will be enrolled in order to further evaluate the safety and efficacy of the combination treatment in these tumor indications.