As a clinical immunologist with a special interest in vaccines, it is a pleasure to present this special issue of Consultant For Pediatricians. Vaccines are among the major achievements of modern medicine. Once common serious childhood illnesses, including tetanus, diphtheria, polio, mumps, and measles, are now rarely seen in this country. It is ironic, therefore, that with the precipitous decline in the incidence of many infectious diseases brought about by widespread vaccination--and the very recent availability of several new vaccines--many parents have been lulled into a false sense of security about the risk posed by the diseases these vaccines have been designed to prevent.