The purpose of this real world non-interventional study is to learn about the effects of etrasimod as treatment for patients with moderate to severe ulcerative colitis.

Patients will be treated according to standard of care and will only be included in the study if etrasimod is the best treatment choice according to the treating physician. Additionally, patients have to be between 18 and 65 years of age and should not have taken etrasimod in the past.

All patients will be prescribed etrasimod according to standard of care. Assessments will be conducted according to standard of care with the exception of health questionnaires which will be completed by the patients online on their own device.

The study duration is 52 weeks with 28 days of safety follow-up. Patients will visit their treating physician as they would if they were not enrolled in the study. During the study duration, patients will be asked to complete health questionnaires on a regular basis either on their mobile phone, tablet or computer.

The effects of etrasimod will be analyzed for each patient comparing to their disease activity prior to the start of etrasimod.

Inclusion Criteria:

• Male and female patients ≥18 and <65 years of age at baseline
• Patients with confirmed diagnosis of ulcerative colitis and who are prescribed etrasimod for moderately to severely active ulcerative colitis as per the product label independently of the decision to enroll a patient in this study.
• Evidence of a personally signed and dated informed consent document indicating that the patient has been informed of all pertinent aspects of the study.

Exclusion Criteria:

• Presence of clinical findings suggestive of Crohn's disease.

• Severe extensive colitis evidenced by:

  1. Physician judgement that the patient is likely to require hospitalization for medical or surgical intervention of any kind for UC (eg, colectomy) within 12 weeks.

  2. Current evidence of acute severe UC, fulminant colitis, or toxic megacolon 3. Patients with a stoma or planned UC surgical intervention requiring hospitalization.

     4. Prior/Concomitant Therapy:

  1. any previous exposure to etrasimod including participation in the etrasimod clinical program.
  2. any co-medication with one of the following conventional therapies: methotrexate or a thiopurine (azathioprine, mercaptopurine or tioguanine) or with any of the following advanced therapies for UC: biologics (a TNF, integrin or cytokine antagonist); JAK inhibitors (filgotinib, tofacitinib or upadacitinib) or with any other S1P receptor modulator.

• Not owning a digital device with internet connection and/or not willing to complete health questionnaires on this device or not capable of using the health questionnaire collection tool.

• Investigator site staff or Pfizer employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family.

Eligible patients can be included in this study if their physician makes a clinical decision to treat them with etrasimod, as defined by the local approved label and independent from the decision to enroll the patient in this study.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.