Appendicitis, diverticulitis, and colitis are common gastrointestinal conditions presenting to the emergency department (ED). Although it is a common condition, the diagnosis of appendicitis remains challenging, and the approach to this disease continues to evolve. The diagnostic approach to diverticulitis is more straightforward, and treatment and the decision whether to hospitalize varies with disease severity. Colitis may be caused by inflammatory bowel disease, ischemia, or infection. This article details an ED-based approach to each of these disease entities.