Ultrasound is a non-invasive, real-time, and radiation-free method of evaluating the bowel. In the context of bowel diseases, ultrasound plays a pivotal role not only in detecting structural and functional abnormalities but also in guiding management decisions. Conditions that may benefit from bowel ultrasound include ischemic colitis, infective colitis, and graft-versus-host disease (GVHD), all of which present with distinct clinical features and require tailored diagnostic approaches. Ischemic colitis, often seen in elderly patients or those with cardiovascular risk factors, results from reduced blood flow to the colon, leading to bowel injury and inflammation. Infective colitis, caused by a variety of pathogens, can range from mild to severe and may lead to complications such as abscess formation and bowel perforation. GVHD, a common complication following hematopoietic stem cell transplantation, involves an immune-mediated attack on the gastrointestinal tract, leading to inflammation, ulceration, and, in some cases, bowel necrosis. Intestinal ultrasound is an effective tool to assess bowel wall thickening, peristalsis, vascular flow, and complications in these disorders. Although it cannot always offer a definitive diagnosis, it may serve as an essential first-line imaging tool, particularly in acute or critically ill patients in whom other imaging modalities might not be immediately available or appropriate. This chapter will explore the ultrasound findings associated with ischemic colitis, infective colitis, and GVHD, highlighting the importance of ultrasound in both the diagnosis and the monitoring of these conditions.