During the past century the U.S. family system has seen vast changes--in marriage and divorce rates, cohabitation, childbearing, sexual behavior, and women's work outside the home. Andrew Cherlin reviews these historic changes, noting that marriage remains the most common living arrangement for raising children, but that children, especially poor and minority children, are increasingly likely to grow up in single-parent families and to experience family instability. Cherlin describes the economic and cultural forces that have transformed family life. Job market changes have drawn married women into the work force and deprived less-educated men of the blue-collar jobs by which they traditionally supported their families. And effective contraception and legalized abortion have eroded the norm of marriage before childbearing. Cherlin notes that sentiment in favor of marriage appears to be stronger in the United States than in other developed countries. The share of U.S. adults who are likely to marry is higher, but so is the share likely to divorce. U.S. children are also more likely to live in single-parent families at some time in their childhood. Although nearly all Americans, whether poor or well-to-do, hold to marriage as an ideal, today marriage is increasingly optional. To a greater extent than ever before, individuals can choose whether to form a family on their own, in a cohabiting relationship, or in a marriage. Given U.S. patterns of swift transitions into and out of marriage and high rates of single parenthood, American policymakers eager to promote marriage are unlikely to be able to raise U.S. family stability to levels typical of other developed countries. Consequently, a family policy that relies too heavily on marriage will not help the many children destined to live in single-parent and cohabiting families--many of them poor--during their formative years. Assistance must be directed to needy families, regardless of their household structure. Policymakers must craft a careful balance of marriage-based and marriage-neutral programs to provide adequate support to American children.