The economic importance of vaccines lies partly in the burden of disease that can be avoided and partly in the competition for resources between vaccines and other interventions. Up to the 1980s only few economic evaluations had been carried out. Since then the confrontation of most countries with escalating health care costs and tighter budgets have awakened the interest in pharmacoeconomic analysis. Resources used to provide health care are vast but not limitless. When clinicians are asked to participate in decisions for large groups of patients (in a managed care context, in an institution, or at the level of local health authorities), the balance between consumption of resources and the benefits of an intervention is important. Clinicians may use cost-effectiveness and cost-benefit studies to inform such decisions (but not to make them). Because of differences in methods, the presentation of results, and country-specific parameters, economic evaluations of the same vaccination strategy by different groups may have divergent results. Vaccines differ from classical medicines in at least three ways: firstly, there is a longer tradition of economic evaluations for vaccines than for medicines. Some of the most earliest economic studies were carried out in the field of vaccines in the public health arena. Secondly, comparatively fewer central decision makers need to be convinced as compared to drugs. The reason for this being a more centralised process of recommending vaccines and vaccination policies. Thirdly, externalities are more relevant in the field of vaccines. Such externalities may be positive or negative. Positive externalities are present in the case where herd immunity prevents the spread of the disease in the community. We are now undoubtedly in an era of assessment and accountability for all new technologies in healthcare. However, sufficient economic data are still lacking to support the formulation of health policy and a particular challenge for the future is to conduct further health economic research on immunisation. Specific areas for such study include: effectiveness under field conditions (i.e., not under the conditions of a randomised controlled trial); the real value of economic production losses; the conditions for implementing novel immunization programmes; cost estimates for more ambitious immunization programmes; the economic benefits of combination vaccines. From this research, it will be important to disseminate the data and to adapt the findings to other countries. Nevertheless, the source of funding for research and its application in clinical trials programmes represent some of the practical problems faced by medical economics today within academia and the industry.