Inclusion Criteria:

• Participants with an endoscopically confirmed diagnosis of active moderate to severe Ulcerative colitis (UC).
• Participants initiating Upadacitinib (UPA) at the investigator's discretion as part of their routine clinical care; the decision to administer UPA must be made prior to and independent of documentation for the study and according to the approved local label.
• Participants able to understand and communicate with the investigator and comply with the requirements of the study.
• Participants willing to continue with study documentation after cessation of UPA.

Exclusion Criteria:

• Participants with any contraindication to Upadacitinib (UPA).
• Participants previously exposed to a Janus kinase (JAK) inhibitor.