Rotaviruses are the single most important cause of severe diarrhea of infants and young children world-wide. Deaths from rotavirus diarrhea occur infrequently in developed countries; however, in developing countries, rotaviruses are estimated to cause over 870000 deaths in the under five-year age group. There is, therefore, a vital need for a vaccine to prevent severe rotavirus diarrhea in infants and young children. The most extensively evaluated strategy for rotavirus vaccination has been the "Jennerian" approach in which an antigenically related rotavirus strain from an animal host (bovine or simian [rhesus monkey]) is used as the immunogen to induce protection against the four epidemiologically important group A human rotavirus serotypes. These orally administered vaccines were safe and immunogenic but had only limited success because serotype-specific immunity was not induced consistently in the under six-month age group. Therefore, a modified "Jennerian" approach was adopted with the goal of attaining broader antigenic coverage. In this approach four serotypes are combined to form a quadrivalent vaccine comprised of (i) rhesus rotavirus (RRV) which provides coverage for VP7 serotype 3, and (ii) three human-RRV reassortants each with ten RRV genes and a single human rotavirus gene that encodes VP7 serotype 1, 2, or 4 specificity. This modified "Jennerian" approach appears to be quite promising in preventing severe diarrhea in field trials. However, if this approach fails to yield an optimal level of protection consistently, additional modified "Jennerian" strategic, are under development that consider not only human rotavirus VP7 but also human rotavirus VP4, the other outer capsid protein. In addition, a non-"Jennerian" approach includes the development of cold-adapted human rotavirus strains or cold-adapted human rotavirus reassortants as vaccine candidates.