• Written informed consent and HIPAA authorization for release of personal health information. NOTE: HIPAA authorization may be included in the informed consent or obtained separately.

• Age \>= 18 years at the time of consent.

• ECOG Performance Status of 0-1 within 28 days prior to registration.

• Patients must have undergone complete surgical resection of their stage I (tumors \>= 4cm), IIA, IIB, and select stage III \[any T1-3 N1-2 and T4N0-2\] NSCLC according to the AJCC 8th edition with negative margins (R0).

• Squamous or non-squamous NSCLC histology. Cancers with a histology of adenosquamous are considered a type of adenocarcinoma and thus non-squamous histology.

• Surgery for this lung cancer must be completed \<= 60 days prior to starting treatment.

• Must have tissue available to perform prospective correlative testing. Tissue block is preferred but 10-15 unstained slides (5 μm thick) are also acceptable. If prior PD-L1 results with Dako 22C3 antibody are not available, an additional 5 unstained slides (4 μm thick) must be submitted.

• Demonstrate adequate organ function as defined in the protocol; all screening labs to be obtained within 28 days prior to registration.

• Females of childbearing potential must have a negative serum pregnancy test within 7 days prior to registration NOTE: Females are considered of childbearing potential unless they are surgically sterile (have undergone a hysterectomy, bilateral tubal ligation, or bilateral oophorectomy) or they are naturally postmenopausal for at least 12 consecutive months

• For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods, and agreement to refrain from donating eggs, as defined below:

‣ Women must remain abstinent or use contraceptive methods with a failure rate of \< 1% per year during the treatment period and for 5 months after the final dose of atezolizumab.

⁃ A woman is considered of childbearing potential if she is postmenarchal, has not reached a postmenopausal state (\> or equal to 12 continuous months of amenorrhea with no identified cause other than menopause), and has not undergone surgical sterilization (removal of ovaries and/or uterus). The definition of childbearing potential may be adapted for alignment with local guidelines or requirements.

⁃ Examples of contraceptive methods with a failure rate of \< 1% per year include bilateral tubal ligation, male sterilization, hormonal contraceptives that inhibit ovulation, hormone-releasing intrauterine devices, and copper intrauterine devices.

⁃ The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or post-ovulation methods) and withdrawal are not acceptable methods of contraception.

• Contraception method must begin starting from the time of informed consent until 5 months after treatment discontinuation.

• For men: Agreement to remain abstinent (refrain from heterosexual intercourse) or use a condom, and agreement to refrain from donating sperm, as defined below:

‣ With female partners of childbearing potential or pregnant female partners, men must remain abstinent or use a condom during the treatment period and for 5 months after the last dose of study treatment to avoid exposing the embryo. Men must refrain from donating sperm during this same period.

⁃ The reliability of sexual abstinence should be evaluated in relation to the duration of the clinical trial and the preferred and usual lifestyle of the patient. Periodic abstinence (e.g., calendar, ovulation, symptothermal, or post-ovulation methods) and withdrawal are not acceptable methods of contraception.

• As determined by the enrolling physician or protocol designee, ability of the subject to understand and comply with study procedures for the entire length of the study