One of the most successful prophylactic interventions in the history of public health, vaccination helped control some of the deadliest and most debilitating infectious diseases. As a result of vaccination programs, smallpox was eradicated worldwide, poliomyelitis was nearly eradicated and emerges as the next eradication target, and national programs helped reduce the incidence of tuberculosis in many countries. Other, more recent vaccines have already achieved a visible impact, as revealed by the ability of the hepatitis B vaccine to decrease the number of new hepatitis infections and the incidence of hepatocellular carcinoma. While vaccination, like any other medical intervention, may have adverse effects, significant controversies gravitated, in recent years, around its supposed link to autism. One of the articles that provided substantial support for this link was recently retracted amid evidence of ample scientific and ethical misconduct. As studies from several countries found that the incidence of autism was increasing even after the removal of thimerosal from vaccines, it appears that, in all likelihood, this trend was not caused by the mercurycontaining preservative, and potential causes have to be pursued somewhere else. Although many early vaccines were prepared empirically from live attenuated or inactivated pathogens, recent years have witnessed a shift toward a more rational strategy, in which concepts from disciplines including molecular biology, genomics, proteomics, and bioinformatics arc increasingly incorporated into vaccine design, transforming vaccinology into a dynamic and vibrant interdisciplinary field.