Key Inclusion Criteria:  Adolescent (12 - 17 years of age) Part A: at time of visit Part B: at time of screening visit Diagnosis of atopic dermatitis (AD) according to American Academy of Dermatology consensus criteria; chronic AD Part A: first diagnosed at least 1 year prior to visit Part B: first diagnosed at least 1 year prior to the screening visit EASI score ≥ 12 Part A: at time of visit Part B: at screening and baseline visits IGA score ≥ 3 Part A: at time of visit Part B: at time of screening and baseline visits Peak Pruritus NRS score ≥ 4 Part A: at time of visit Part B: at time of screening and baseline visits as defined in the protocol The CPT-3 d' score for entry into Part B will be determined based on the distribution of the CPT-3 d' score from Part A BSA of AD involvement ≥ 10% Part A: at time visit Part B: at screening and baseline visits Part B Only: Documented recent history (within 6 months of the screening visit) of inadequate response (in the opinion of the investigator) to topical AD medication(s) or for whom topical AD medications are medically inadvisable as defined in the protocol Part B Only: Patient's stable use of a prescription topical medication regimen for AD lesions for at least 2 weeks prior to baseline as defined in the protocol  Key Exclusion Criteria:  Prior use of dupilumab Part A: within 6 months of visit Part B: within 6 months of screening Skin diseases that could confound AD assessment as defined in the protocol Treatment with methylphenidate, dexmethylphenidate, serdexmethylphenidate, amphetamine, dextroamphetamine, lisdexamfetamine, guanfacine, atomoxetine, clonidine, or viloxazine within 8 weeks or within 5 half-lives, whichever is longer, at visit History of clinician-diagnosed attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder, epilepsy, major depressive disorder, mania or bipolar disorder, or any Diagnostic and Statistical Manual-V (DSM-V) psychotic disorder, such as schizophrenia Evidence of substance abuse, including alcohol and nicotine, in the past 2 years Systemic antihistamine or nicotine use Part A: within the week prior to the visit Part B: during the week prior to screening Part B Only: Active helminthic infections; suspected or high risk of helminthic infection, unless clinical and (if necessary) laboratory assessments have ruled out active infection before baseline Part B Only: At baseline, presence of any conditions listed as criteria for study drug discontinuation Part B Only: Treatment with high potency or super-potent TCS within 14 days prior to baseline  NOTE: Other protocol defined inclusion/exclusion criteria apply