This paper reviews key contributions to the psychology and economics literature on willpower. Understanding how willpower develops can shed important light on time-inconsistent economic decision making, a topic that has received substantial attention over recent decades. In particular, we argue that measures of willpower for the child provide useful insights into the nature of willpower and are reliable predictors of economic outcomes in the adult. The implication is that one might, for example, be able to strengthen a "weak" child's ability to resist temptation, and in so doing offer welfare enhancements not only to the child but also to the ultimate adult decision maker. Finally, we list a set of open questions that could be profitably addressed by the future research.