Prevention of disease by vaccination has been one of the major triumphs of medicine. Studies have been done on many vaccines to determine their benefits, risks, and costs. These studies have demonstrated that the benefits outweigh the risks and costs for many vaccines including polio, pertussis, measles, mumps and rubella. Thus, the use of these vaccines provides a net saving to society. Other vaccines such as those influenza and pneumococcal disease are cost-effective relative to other health expenditures. The value of benefit-risk, benefit-cost, and cost-effectiveness analyses lies not in providing the definitive basis for a decision on vaccine use or evaluation. Rather, these analytic techniques provide a structured framework which permits decision-makers to consider all relevant components of the decision in perspective to their relative contributions and subsequent effects. It forces key assumptions to be made explicit and identifies areas in which data are inadequate. The results of such analyses can assist in justifying a vaccination programme (poliomyelitis), in disseminating a programme more widely (measles), in changing health policy (smallpox), and in planning for how a vaccine might be used (hepatitis B). Cost analyses of vaccination may suggest the value of a vaccination programme, but the programme may not be widely adopted (influenza and pneumococcal vaccines). The reasons for this gap between study conclusions and application may be: disagreement with the estimates and assumptions used in the analysis; skepticism over the methodology itself; or subjective views of the vaccine or disease which remains resistant to analytical exercises.