Economists know a lot about individuals' behavior in markets. They have developed theories that explain how individuals respond to change in their economic environment. For example, theory predicts that changes in Social Security that reduce the value of benefits will induce workers to delay retirement. Empirical studies show that prediction is borne out by the data. But there are many areas where economists and other social scientists have well developed theories, but little or no empirical evidence. For example, once people retire, theory predicts that they will engage in more nonmarket production, but there are no data with which to test this hypothesis. In other cases, interesting questions have gone unanswered because of lack of data. For example, how would the distribution of family income be affected if we accounted for the nonmarket production of non-working spouses? In this paper, we discuss some of the uses of time-use data in the context of these and other unanswered questions.