A Study Evaluating the Safety and Pharmacology of Atezolizumab Administered in Combination With Immunomodulatory Agents in Participants With Acute Myeloid Leukemia (AML)

Inclusion Criteria:

* Life expectancy of at least 12 weeks
* Diagnosis of AML per World Health Organization criteria
* Eastern Cooperative Oncology Group (ECOG) performance status score of 0, 1 or 2
* Specifically, for participants in Cohorts A1 and A2: Age greater than or equal to (\>=) 18 years, disease progression or failure to achieve complete or partial response after intensive cytotoxic therapy, participants cannot have received more than two prior intensive regimens (e.g., induction + consolidation and one salvage therapy + consolidation)
* Specifically, for participants in Cohorts A3 and A4: Treatment naïve participants unfit for induction chemotherapy for AML as defined by the following: Age \>= 70 or age 65 to 69 years with at least one of the following: ECOG performance status of 2, Intermediate I/II or adverse risk cytogenetic and molecular alterations per ELN 2010 guidelines or secondary AML, or other comorbidity judged incompatible with intensive chemotherapy
* Adequate end-organ function
* Willing and able to undergo a pre-treatment bone marrow aspirate and biopsy and subsequent bone marrow aspirates and biopsies during treatment
* For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods that result in a failure rate of less than (\<) 1 percent (%) per year during the treatment period and for at least 30 days after the last dose of guadecitabine or 5 months after the last dose of atezolizumab, whichever is longer
* For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating sperm

Exclusion Criteria:

* In Cohorts A3 and A4 only, participants with AML eligible for standard intensive induction therapy with an anthracycline and cytarabine
* Prior allogeneic stem cell transplant or solid organ transplant
* Active central nervous system involvement by leukemia
* Pregnant or lactating, or intending to become pregnant during the study
* History of idiopathic pulmonary fibrosis, organizing pneumonitis, drug-induced pneumonitis, idiopathic pneumonitis, or autoimmune disease
* Treatment with investigational therapy within 14 days prior to initiation of study drug
* Any approved AML-related therapy within 14 days prior to enrollment
* Immunosuppressive therapy within 6 weeks of Cycle 1, Day 1
* Daily requirement for corticosteroids (\> 10 mg prednisone daily or equivalent) (except for inhalation corticosteroids) within 2 weeks prior to Cycle 1, Day 1
* Prior treatment with immune checkpoint blockade therapies (anti-cytotoxic T-lymphocyte-associated protein 4 \[anti-CTLA-4\], anti-programmed death-1 \[anti-PD-1\] or anti-PD-L1) or immune agonists (anti-cluster of differentiation \[CD\]137, anti-CD40, anti-OX40)
* Treatment with systemic immunostimulatory agents within 4 weeks or 5 half-lives of the drug, whichever is longer, prior to Cycle 1, Day 1
* Treatment with denosumab (or other receptor activator of nuclear factor kappa-B ligand \[RANKL\] inhibitor) 4 weeks before the first dose and for 10 weeks after the last dose of atezolizumab
* Administration of a live, attenuated vaccine within 4 weeks of Cycle 1, Day 1 or anticipation that such a live attenuated vaccine will be required during the study
* Planned major surgery during the study
* Positive for hepatitis C virus (HCV) antibody at screening
* Active hepatitis B virus (HBV) infection
* Positive for human immunodeficiency virus (HIV)
* Illicit drug or alcohol abuse within 12 months prior to screening
* Poor peripheral venous access
* Active infection
* Serious infection requiring hospitalization or intravenous (IV) antibiotics within 14 days prior to enrollment
* Any serious medical condition or abnormality in clinical laboratory tests
* History or presence of an abnormal electrocardiogram (ECG)
* History of other malignancy within 2 years prior to screening
* Known hypersensitivity to biopharmaceuticals produced in Chinese hamster ovary cells or any component of the atezolizumab or guadecitabine formulations
* History of severe allergic, anaphylactic or other hypersensitivity reactions to chimeric or humanized antibodies or fusion proteins