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:

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  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.