A Study to Observe Real-world Evidence of Guselkumab Treatment in Participants With Ulcerative Colitis and Crohn's Disease in the United Kingdom (UK)

Inclusion Criteria: * Must be eligible for biologic treatment and initiate guselkumab according to the approved indications as described in the current version of the summary of product characteristics (SmPC) of the drug. Decision to prescribe must solely be made by the treating physician in line with the Trust's/ Health Board's treatment guidance. Enrolment must take place before or at the day of first administration (but after treatment decision by physician) * Must have a confirmed diagnosis of moderate-to-severe Crohn's Disease (CD) or Ulcerative Colitis (UC) recorded in their medical records * Must sign a informed consent form (ICF) allowing source data verification in accordance with local requirements Exclusion Criteria: * Contraindicated to guselkumab per the label * Is currently enrolled in an interventional clinical study * Has been previously exposed to interleukin (IL)-23 inhibitors, including Tremfya® (guselkumab), Skyrizi ® (risankizumab) and Omvoh® (mirikizumab). As an exception, participants with history of ustekinumab exposure, may be included * Has a history of more than 4 lines of advanced inflammatory bowel disease (IBD) therapy (biologics and /or small molecules) * Is unable to provide informed consent