The unions of unwed parents are referred to as "fragile families" because they are similar to traditional families in many respects, but are more vulnerable. The Fragile Families and Child Wellbeing Study (FFS) is designed to study such families by following a new birth cohort of approximately 4,700 children, including 3,600 children born to unmarried parents. This new data will be representative of nonmarital births in each of 20 cities and in U.S. cities with populations over 200,000. Both mothers and fathers will be followed for at least 4 years, and in-home assessments of children's health and development will be carried out when the child is 4 years old. The survey is designed to address the following questions: (1) What are the conditions and capabilities of new unwed parents, especially fathers? (2) What is the nature of the relationships in fragile families? (3) What factors push new unwed parents together and what factors pull them apart? and (4) How do children fare in fragile families, and how is their wellbeing affected by parental capacities and relationships and by public policies? This paper describes what is currently known about each of the questions and describes how the FFS addresses each of them. It also presents some preliminary findings based on data from Austin, Texas and Oakland, California. (Contains 1 map, 6 tables, and 65 references.) (SLD)