Recent economic explanations of changes in fertility behaviour have focussed on the effects of labour-market-related incentives. The present paper draws attention to another set of incentives, those connected with the transfer of resources over time. The theoretical implications of intergenerational altruism as a possible motive for having children and making transfers to them are considered, and contrasted with those arising from the competing hypothesis that such actions are motivated by old-age-security considerations. From a comparison of these theoretical predictions with the findings of a number of empirical studies, it would appear that self-interested concern for one's old age, rather than any great love for future members of one's dynasty, is or has been so far the dominant force driving fertility and intergenerational transfers worldwide.There is a saying that the population of the world can be divided into two -those who starve and those who diet. To this one could add that, in those parts of the world where there are people who starve, there is also a population explosion problem, while in more affluent parts, where there are people who worry about their waistline, the problem is population ageing. As economists, we tend to explain these demographic differences in terms of differences in the structure of incentives. Much has been made, for example, of the effects of labour-market-related incentives on fertility and life-expectancy. In this address, I shall focus on another set of incentives, those pertaining to the intertemporal allocation of resources. Besides contributing to the understanding of the important issues that I have mentioned, this approach will allow me to draw together two apparently unrelated