This randomized, double-blind, placebo-controlled study will evaluate the safety and efficacy of lebrikizumab administered subcutaneously (SC) in adult participants with persistent moderate to severe atopic dermatitis (AD) who are inadequately controlled by topical corticosteroids (TCS). The study includes a screening visit, a 2-week run-in period, a 12-week blinded treatment period, and an 8-week safety follow-up period. Following screening visit, eligible participants will enter in run-in period (Days − 14 to − 1) during which a protocol-specified topical therapy regimen will be initiated. At the end of the run-in period, participants who have: 1) demonstrated compliance with the protocol-specified TCS regimen, and 2) who continue to fulfill the eligibility criteria will be randomized.