One of the largest child welfare systems in the United States caring for tens of thousands of children in its foster care system is New York City's Administration for Children's Services (ACS). ACS has contracted with about 60 private foster care providers with a wide variety of placements. This study sought to provide child welfare managers with a data-driven, longitudinal view of trends in New York City's child welfare system. Due to the City's size and complexity, the study was narrowed and identified three critical questions facing ACS managers, along with three analytic techniques suggesting answers to the questions. The three questions included: (1) who was in foster care, and what services were likely needed; (2) how frequently do children move to new placement, and when they move, what type of placements are they coming from and going to; and (3) are the characteristics and patterns of children leaving care without permission? The three principal descriptive techniques used to study the questions were point-in-time or snapshot studies, trend analysis, and cohort analysis. To provide a comprehensive picture, all three techniques were used for the analysis. Three key findings of the analyses include: (1) ACS is caring for a significantly older population than 10 years ago; (2) entries into foster care are a critical input; and (3) the typical foster child does not runaway from care, have multiple spells in care, or experience repeated movement to new facilities. The findings have several implications: (1) to respond to the instability in the types of children in care by creating more flexible placements that could adapt as the foster care population changes; (2) to expand the use of therapeutic foster bed homes and supervised independent living programs; (3) to streamline the discharge process; and (4) to focus on early interventions for children likely to develop multiple spells and AWOL activity. Figures, tables, bibliography, and Appendices A and B