Rotaviruses are the most common cause of severe, dehydrating diarrhea in children worldwide. The tremendous global incidence of rotavirus gastroenteritis, especially in developing countries, emphasizes the need for vaccines to prevent associated morbidity and mortality. However, immunity to rotavirus is not completely understood. At this time, total serum RV IgA, measured shortly after infection, appears to be the best marker of protection against rotavirus. This review describes the current understanding of rotavirus immunity, including mechanisms of protection against rotavirus from selected animal models, and correlates of protection associated with natural infection or vaccination from humans.