In this chapter, I emphasise and try to explain the importance of historical demography for economic history, but also its relative neglect by ancient historians until very recently. Demography involves a range of quantitative measures that are useful both as proxies for economic performance and in comparison. Population sizes and trends also have explanatory power for past economic changes. Some general points about the relationship between population and economy, and what changed and what stayed the same over the last millennium BCE are followed by some more specific observations about the major periods of Greek history. The importance of environmental factors is particularly emphasised, and urbanization is a persistent theme.