The articles in this issue of the International Journal of Technology Assessment in Health Care (IJTAHC) have explored the assessment of preventive health technologies. When considered together, these technologies provide an interesting contrast with the health care technologies that are usually evaluated on these pages. Disease prevention and its twin, health promotion, are usually practiced on a well population. Thus, many persons have the technology applied to them but only a fraction of these would have acquired the condition being prevented. Often the intervention is applied to populations rather than to individuals. The unit cost for preventive technologies is usually far less than that of diagnostic or therapeutic technologies. However, when multiplied by the larger population to be involved in the prevention program, the total costs can be considerable. In concluding this section on prevention, we would like to examine some of the larger areas of difference between preventive and other health technologies illustrated by the papers assembled here.