Viral gastroenteritis is among the most common illnesses affecting humans and has greatest impact at the extremes of age. The spectrum of disease can range from asymptomatic infections to severe disease with dehydration. In contrast to bacterial pathogens, enteric viruses cannot multiply outside their host; hence, the original inoculum into the common source determines infectivity. Prevention of contamination of food and water control primary cases, whereas careful nursing and handwashing prevent secondary cases. Effective vaccines are available and widely used to prevent rotaviral gastroenteritis, but vaccines for other causes of viral gastroenteritis are not yet available.