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.