The colon is susceptible to many infectious pathogens including bacteria, fungi, viruses, and parasites. Although Clostridium difficile infection is the most common cause of infectious colitis in Western countries, other infections are an important cause of morbidity and mortality. Bacterial colitides are a frequent cause of food-borne illness in the United States. Viral and fungal colitis can cause life-threatening illness, especially in the immunocompromised patient. In third-world countries, and in patients traveling abroad, infectious colitis from bacteria and parasites is important to understand. Infectious colitides play a major role in patients with inflammatory bowel disease, AIDS, and organ transplants.