In this thesis we investigated the role of intestinal ultrasound (IUS) for the monitoring of inflammatory bowel disease (IBD). IBD, both Crohn’s disease (CD) and ulcerative colitis (UC), is a chronic inflammatory disease of the intestinal tract with a relapsing-remitting pattern. As endoscopy is considered the gold standard to diagnose and assess state of inflammation, IBD patients often undergo frequent endoscopic examinations along disease course. However, endoscopy is not without risks, comes with significant burden to the patient and is expensive. IUS is a non-invasive, fast and cheap alternative but currently lacks standardization and is therefore not frequently used. In this thesis we standardized the IUS technique and measurements with high reliability among expert ultrasonographists to assess inflammation in both CD and UC. Furthermore, we compared endoscopic disease activity to IUS measurements and found high correlation. Predominantly bowel wall thickness (BWT) and hypervascularity of the bowel wall correlate moderately to perfectly with endoscopic disease activity scores in both CD and UC. Subsequently, patients were treated and response to treatment was measured with both endoscopy and IUS. We showed that IUS is accurate to determine endoscopic treatment response. In addition IUS detected response to treatment already two to eight weeks after treatment initiation. In conclusion, IUS allows fast, accurate and reliable assessment of inflammation and treatment response. It thereby allows tight monitoring in a point-of-care setting and could function as a surrogate marker for endoscopy in most patients.