Building Strong Families (BSF) is a large-scale demonstration and rigorous evaluation of marriage and relationship education programs that has now enrolled more than 5,000 low-income, romantically involved, unmarried couples. At enrollment, all couples were expecting or recently had a child together. This report highlights key findings from an implementation analysis of BSF’s seven program sites in Atlanta, Baltimore, Baton Rouge, Florida, Indiana, Oklahoma, and Texas during the evaluation's first 6 to 14 months. The analysis documents recruitment and enrollment practices, describes the characteristics of enrolled couples, provides data on program participation, and summarizes the experiences of couples participating in the intervention. Individuals who enrolled in the program were typically in their mid-twenties, and often had children from prior relationships. While most had a high school education, earnings and income were low. Over half the recruited sample members were African American, about one-quarter were Hispanic, and about 14 percent were non-Hispanic white. The average couple had known each other for several years, was cohabiting, and had high hopes for marrying their partner.