Making a commitment in advance to buy vaccines if and when they are developed would create incentives for industry to increase investment in research and development. New commercial investment would complement funding of research and development by public and charitable bodies, accelerating the development of vital new vaccines for the developing world. This report presents the proposal from theory to practice, by showing how a commitment can be consistent with ordinary legal and budgetary principles. By creating arrangements that devote the same scientific effort to diseases of the poor as we put into diseases of the rich, we can make a lasting contribution to the defeat of poverty.