Policy-makers and lay-people alike know that health-care costs have risen considerably and continue to rise. However, myths and misunderstandings often shape any debate as the underlying factors, their effects and interactions may not be well-understood. Ageing or (more broadly) the demographic transition, is the most often quoted driver although economic growth and the resulting higher incomes; medical progress through innovation and new technologies; health-care organization and financing; higher relative prices for health-care inputs; and the increasing expectations of citizens can all lead to higher expenditure. This chapter reviews recent research and evidence in order to provide an assessment of the present and potential future impacts of these drivers on health expenditure.