Ulcerative colitis (UC) is an idiopathic, chronic, inflammatory disease affecting the colon. Crohn's disease (CD) is an incurable chronic inflammatory disorder of the gastrointestinal tract. This study will assess how safe and effective upadacitinib is in treating adult participants with moderate to severe ulcerative colitis and Crohn's disease. Adverse events and change in disease activity will be assessed. Upadacitinib is an approved drug for treating Atopic dermatitis (AD), psoriatic arthritis (PsA), ankylosing spondylitis (AS), non-radiographic axial spondyloarthritis (nr-axSpA), ulcerative colitis (UC), and Crohn's disease (CD). Approximately 600 adult participants who are prescribed Upadacitinib by their physician in accordance with local label will be enrolled in Korea. Upadacitinib will be administered in accordance with the terms of the local marketing authorization, and treatment of participants will be determined solely by the investigator. Participants in the study will be followed for up to 52 weeks. There is expected to be no additional burden for participants in this trial. Participants will attend regular visits during the study at a hospital or clinic according to their routine clinical practice.