We describe the promise of the Fragile Families and Child Wellbeing Study (FFCWS) for developmental researchers. FFCWS is a birth cohort study of 4,898 children born in 1998–2000 in large US cities. This prospective national study collected data on children and parents at birth and during infancy (age 1), toddlerhood (age 3), early childhood (age 5), middle childhood (age 9), adolescence (age 15), and, in progress, young adulthood (age 22). Though FFCWS was created to understand the lives of unmarried parent families, its comprehensive data on parents, children, and contexts can be used to explore many other developmental questions. We identify six opportunities for developmentalists: (a) analyzing developmental trajectories, (b) identifying the importance of the timing of exposures for later development, (c) documenting bidirectional influences on development, (d) understanding development in context, (e) identifying biological moderators and mechanisms, and (f) using an urban-born cohort that is large, diverse, and prospective.