Acute gastroenteritis (AGE) is an illness caused by viral, bacterial, or parasitic infection of the intestinal tract. Illness is most common among children, but patients of all ages are affected to some degree. With the use of new diagnostics, there is increasing recognition of a widening array of enteric pathogens associated with acute gastroenteritis. The etiology of AGE varies with geographic location, time of year, and the population studied. Many enteric pathogens are easily transmitted through food or water or from one person to another, and some can be devastating to individuals with compromised immune systems. Adequate fluid and electrolyte replacement and maintenance followed by early refeeding are the keys to effective management. A complete clinical and epidemiologic evaluation, in addition to assessment of possible exposures and whether the patient is immunocompromised, will direct the performance of diagnostic studies and the administration of antimicrobial therapy. Important measures to prevent the spread of enteric pathogens include proper sanitation methods for food processing and preparation, sanitary water supplies, pasteurization of milk, proper hand hygiene, sanitary sewage disposal, exclusion of infected people from handling food or providing health care, and exclusion of people with gastroenteritis from use of public recreational water.