Like previous editions, the third edition of Why Marriage Matters reviews the relevant research on family topics and comes to three fundamental conclusions: marriage is an important social good, marriage is an important public good, and the benefits of marriage extend to poor and minority communities. The third edition pays particular attention to new research on the impact of cohabitation on children and families. It concludes with a “U.S. Marriage Index,” which compiles and presents the leading indicators of marital health in the United States. These indicators include: 1) The percentage of adults marriage (ages 20-54); 2) the percentage of married persons “very happy” with their marriage (ages 18 and up); 3) the percentage of first marriages intact (ages 20-59); 4) percentage of births to married parents; and 5)  the percentage of children living with own married parents.