Does democracy improve the quality of life for its citizens? Scholars have long assumed that it does, but recent research has called this orthodoxy into question. This article reviews this body of work, develops a series of causal pathways through which democracy might improve social welfare, and tests two hypotheses: (a) that a country's level of democracy in a given year affects its level of human development and (b) that its stock of democracy over the past century affects its level of human development. Using infant mortality rates as a core measure of human development, we conduct a series of time-series-cross-national statistical tests of these two hypotheses. We find only slight evidence for the first proposition, but substantial support for the second. Thus, we argue that the best way to think about the relationship between democracy and development is as a time-dependent, historical phenomenon.