Inclusion Criteria:  Has moderately to severely active CD with a bowel wall thickness (BWT) of >3 mm, based on IUS. Newly initiating IV vedolizumab induction treatment in accordance with the current SmPC (switch to SC is acceptable at maintenance treatment stage).  Exclusion Criteria:  Contraindications to vedolizumab therapy as defined in the current SmPC:  Prior history of intolerability, hypersensitivity to the active substance or to any of the excipients of vedolizumab Active severe infections such as tuberculosis (TB), sepsis, cytomegalovirus, listeriosis, and opportunistic infections such as Progressive Multifocal Leukoencephalopathy (PML) Cognitive incapacity, unwillingness or language barriers precluding adequate understanding or cooperation. Current or planned participation in an interventional clinical trial for CD within the past 30 days. Active perforating complications (fistulizing CD), current strictures (definition >50% reduction of bowel lumen and pre-stenotic dilatation) as well as historic strictures (based on medical chart). Characteristics precluding IUS visualization of affected bowel segments or normal BWT of <=3 mm for all segments.