Marriage between two parents, compared with other family living arrangements, appears, on average, to enhance children’s wellbeing and development. Some of the positive association between marriage and children’s wellbeing comes from positive associations between marriage and other things that also contribute to children’s wellbeing. David Ribar first sets up a standard economic rational-choice model to show that, all else equal, marriage should produce advantages that can improve children’s wellbeing, such as better coordination between parents and economies of scale that make limited resources go further. Digging more deeply, he then examines specific mechanisms through which marriage may operate to improve children’s lives. Some of these have been well studied, including income, fathers’ involvement, parents’ physical and mental health, parenting quality, social supports, health insurance, home ownership, parents’ relationships, bargaining power, and family stability. Others have received less attention, including net wealth, borrowing constraints, and informal insurance through social networks. Many of these mechanisms could be bolstered by public policy; that is, when they are lacking in children’s lives, public policy could potentially provide substitutes—greater cash assistance, more generous health insurance, better housing, more help for caregivers, etc. Yet studies of child wellbeing that control for the indirect effects of these mechanisms typically find that direct positive associations remain between children’s wellbeing and marriage, strongly suggesting that marriage is more than the sum of these particular parts. Thus, Ribar argues, the advantages of marriage for children’s wellbeing are likely to be hard to replicate through policy interventions other than those that bolster marriage itself. © 2015 by The Trustees of Princeton University, All rights reserved.