Enteric infections kill approximately two million children under the age of 5 in developing countries and cause more than four billion disease episodes worldwide each year. In addition, these diseases affect the growth, cognitive function, and quality of life negatively. There is an urgent need for vaccines that induce effective and long-lasting intestinal immunity against diarrheal infections, especially during infancy and early childhood. Yet, most vaccines available are formulated on an empirical basis. To date, arguably, vaccines have done more for immunologists than immunologists have done for vaccines.