Atopic dermatitis (AD) is a skin condition that may cause a rash and itching due to inflammation of the skin. Therapies spread over the skin may not be enough to control the AD in trial participants who require systemic anti-inflammatory treatment. This study will assess the real-world effectiveness of upadacitinib on early and sustained response along adolescent and adult participants with AD. This study also aims to understand upadacitinib utilization patterns in real-world clinical practice. Upadacitinib (RINVOQ) is approved in the EU for the treatment of moderate to severe AD in adults and adolescents 12 years and older who are candidates for systemic therapy. Approximately 772 adolescent and adult participants with AD will be enrolled at up to 200 sites in Germany. Participants will receive oral upadacitinib tablets as prescribed by the physician prior to enrolling in this study in accordance with the terms of the local marketing authorization and professional and reimbursement guidelines with regards to dose, population, and indication. The overall duration of the study is approximately 2 years. Participants will attend regular visits per routine clinical practice. The effect of the treatment will be checked by medical assessments, checking for side effects, and questionnaires.