A Phase 1b Study of Atezolizumab in Combination With Erlotinib or Alectinib in Participants With Non-Small Cell Lung Cancer (NSCLC)

Inclusion Criteria:

* Histologically or cytologically documented, locally advanced or metastatic NSCLC.
* Participants in Stage 1 (Safety Evaluation) receiving erlotinib: No limit to the number of prior therapies (except for EGFR TKIs).
* Participants in Stage 2 (Expansion) receiving erlotinib: i) sensitizing mutation in the EGFR gene and ii) consent to collection of tumor tissue samples before, during, and after treatment for biopsy and PD biomarker analyses.
* Participants receiving alectinib in either Stage 1 or Stage 2: must be ALK positive as assessed by Food and Drug Administration (FDA) approved test and must not have received prior treatment for their advanced NSCLC.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* Life expectancy of at least 12 weeks.
* Measurable disease, as defined by RECIST Version 1.1 (v1.1).
* Adequate hematologic and end-organ function.
* Use of highly effective contraception (as defined by protocol) and until 5 months after the last dose of atezolizumab and for 3 months after the last dose of alectinib or for 2 weeks after the last dose of erlotinib, whichever is longer; Males must also refrain from sperm donatation during this same time period. Participants must not be pregnant or breastfeeding.
* Archival tumor tissue specimen meeting protocol specifications or the participant will be offered the option of a pre-treatment biopsy to obtain adequate tissue sample.

Exclusion Criteria:

* For participants receiving erlotinib group: prior treatment with any EGFR mutant-targeting TKI
* Any approved anticancer therapy, including chemotherapy, or hormonal therapy (except hormone-replacement therapy or oral contraceptives) within 3 weeks of first dose.
* Treatment with any other test drug or participation in another clinical trial within 28 days of enrollment.
* Known symptomatic central nervous system (CNS) metastases. Participants with a history of treated or untreated asymptomatic CNS metastases may be eligible.
* Leptomeningeal disease.
* Uncontrolled tumor-related pain.
* Uncontrolled pleural effusion, pericardial effusion, or ascites requiring drainage at least once monthly.
* High levels of calcium requiring bisphosphonate therapy or denosumab.
* Malignancies other than NSCLC within 5 years prior to enrollment, with the exception of those with a negligible risk of metastasis or death (such as adequately treated carcinoma in-situ of the cervix, basal or squamous cell skin cancer, localized prostate cancer, or ductal carcinoma in situ).
* History of severe allergic, anaphylactic, or other reactions to chimeric or humanized antibodies or fusion proteins.
* Known hypersensitivity to biopharmaceuticals produced in Chinese hamster ovary cells or any component of the atezolizumab formulation.
* History of autoimmune disease.
* Participants with prior bone marrow or solid organ transplantation.
* History of lung inflammation or disease.
* Serum albumin less than (\<) 2.5 grams per deciliter (g/dL).
* Positive for Human Immunodeficiency Virus (HIV).
* Liver disease.
* Current or active tuberculosis, hepatitis B, or hepatitis C.
* Participants with past or resolved hepatitis B virus (HBV) infection are eligible; participants positive for hepatitis C virus (HCV) antibody are eligible only if polymerase chain reaction (PCR) is negative for HCV Riboxy Nucleic Acid (RNA).
* Signs or symptoms of infection within 2 weeks prior to first dosing.
* Received therapeutic oral or IV antibiotics within 2 weeks prior to first dosing.
* Significant cardiovascular disease.
* Major surgical procedure other than for diagnosis within 28 days prior to first dosing or during the course of the study.
* Administration of a live, attenuated vaccine within 4 weeks before first dosing or during the study.
* Any other diseases, metabolic dysfunction, physical examination finding, or clinical laboratory finding that may reasonably prevent the participant from participating.
* Hypersensitivity to erlotinib or alectinib or to any of the excipients.
* Any significant ophthalmologic abnormality. The use of contact lenses is not recommended during the study.
* For participants receiving alectinib: baseline Fridericias corrected QT interval (QTcF) greater than (\>) 470 milliseconds (ms) or symptomatic bradycardia.
* Prior treatment with CD137 agonists or immune checkpoint blockade therapies.
* Treatment with systemic immunostimulatory agents within 6 weeks or five half-lives of the drug, whichever is shorter, prior to first dosing.
* Treatment with systemic immunosuppressive medications within 2 weeks prior to first dosing (inhaled corticosteroids and mineralocorticoids are allowed).
* Participants who received acute, low-dose systemic immunosuppressant medication or a one-time pulse dose of systemic immunosuppressant medication are elgible for study after discussion and approval by the Medical Monitor.