Economic theories of childbearing relate decisions about family size and the timing of births over people's lives to elements of the constraints on choice that people face, particularly prices and incomes. This article presents the basic concepts and approaches used in these theories, discusses their main lines of argument, and summarizes some of their empirical implications. It first examines ‘static’ theories of completed family size and then discusses dynamic theories of the timing of childbearing. While mainly concerned with theories of marital fertility, it concludes with a discussion of nonmarital fertility.