An analysis of the welfare, child support, and labor market environments in the first seven Fragile Families cities confirms that, as intended, these cities represent the extremes in terms of their social policies and labor markets. Studying families in cities with extreme environments—generous or stingy welfare policies, strict or lenient child support enforcement, tight or slack labor markets—will allow us to better understand how policies and labor markets interact to affect the living arrangements and wellbeing of families. Based on our theoretical framework, we expect to find more marriage and cohabitation in cities with stingy welfare benefits and policies, strict child support enforcement, and strong labor markets. In contrast, we expect less marriage and cohabitation in cities with generous and accessible welfare benefits, weak child support enforcement, and weak labor markets. In future papers, Fragile Families data in twenty cities will be brought to bear on these predictions.