Ulcerative colitis (UC) is a type of inflammatory bowel disease that causes inflammation and bleeding from the lining of the rectum and colon (large intestine).This study will assess how effective upadacitinib is in treating UC. Upadacitinib (RINVOQ) is an approved drug for treating UC. Approximately 400 adult participants who are prescribed Upadacitinib by their physician in accordance with local label will be enrolled in Germany, Austria and Switzerland. 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 2 years. There will be no additional burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic and only data which are routinely collected during a regular visit will be utilized for this study.