All over the industrialized world, marriage is in decline. Cohabitation, which has waxed as marriage has waned, is a much less stable relational form. In the US, half of all cohabiting relationships dissolve within eighteen months; in both North America and Europe, children born to cohabiting parents are two to four times more likely to experience their parents’ separation than are children born to married parents. This paper critically examines current economic and cultural explanations for these phenomena. It then analyzes the public-policy implications of the available evidence. Formal marriage is associated with a range of benefits to adult partners and their children. Cross-national surveys show that marriage is associated with higher levels of subjective well-being throughout the industrialized and nonindustrialized world. Because the decline of marriage results from a number of different factors, policymakers face large difficulties in reversing the trend. These policy-making difficulties are magnified because the personal benefits of marriage are concentrated in long-term, harmonious marital relationships. (Author abstract)