A Study of the Efficacy and Safety of Upadacitinib in Participants With Moderately to Severely Active Crohn's Disease Who Have Inadequately Responded to or Are Intolerant to Conventional and/or Biologic Therapies

* Confirmed diagnosis of CD for at least 3 months prior to Baseline. * Confirmed diagnosis of moderate to severe CD as assessed by stool frequency (SF), abdominal pain (AP) score. * Evidence of mucosal inflammation based on the Simplified Endoscopic Score for Crohn's disease (SES-CD) on an endoscopy confirmed by a central reader. * Demonstrated an inadequate response or intolerance to one or more conventional and/or biologic therapies (oral locally acting steroids, intravenous or oral corticosteroids, immunosuppressants or biologic therapies for CD), in the opinion of the investigator. * Note: Participants who have had inadequate response or intolerance to conventional therapy who have received prior biologic may be enrolled; however, participants must have discontinued the biologic for reasons other than inadequate response or intolerance (e.g., change of insurance, well controlled disease). * If female, participant must meet the contraception recommendations.

* Participant with a current diagnosis of ulcerative colitis or indeterminate colitis. * Participant not on stable doses of CD related antibiotics, oral aminosalicylates, corticosteroids or methotrexate (MTX). * Participant with the following ongoing known complications of CD: abscess (abdominal or peri-anal), symptomatic bowel strictures, fulminant colitis, toxic megacolon, \> 2 entire missing segments of the following 5 segments: terminal ileum, right colon, transverse colon, sigmoid and left colon, and rectum, or any other manifestation that might require surgery while enrolled in the study. * Participant with ostomy or ileoanal pouch. * Participant diagnosed with conditions that could interfere with drug absorption including but not limited to short gut or short bowel syndrome. * Screening laboratory and other analyses show abnormal results.