As Congress considers reauthorization of the laws which provide funding for the Child Care and Development Fund (CCDF), there is interest in understanding what accounts for recent trends in child care subsidy receipt among eligible families and what research says about subsidies' effects on parents' ability to obtain and maintain employment. The U.S. Department of Health and Human Services (HHS) administers CCDF, but states have flexibility in its implementation. As requested, GAO examined: (1) trends in federal estimates of the number and proportion of eligible children and families who receive child care subsidies, (2) factors that may affect trends in estimates of the number of children served, and (3) what is known about the extent to which access to subsidies supports low-income parents' employment. To address these issues, GAO reviewed recent federal estimates of the number and proportion of eligible children and families served; conducted a survey of state child care administrators in 50 states and the District of Columbia; interviewed HHS officials, state officials in four selected states, and researchers and experts in child care subsidies; and reviewed research on the relationship between subsidy receipt and employment outcomes. GAO is not making recommendations in this report. HHS generally agreed with the report and provided technical comments, which GAO incorporated as appropriate. Five appendices are included: (1) Objectives, Scope and Methodology; (2) Data Reliability Assessment for CCDF Administrative Data and Child Care Subsidy Coverage Rates; (3) Studies Examining the Effect of Child Care Subsidies on Employment Outcomes; (4) Comments from the U.S. Department of Health and Human Services; and (5) GAO Contact and Staff Acknowledgments. (Contains 2 tables, 14 figures and 46 footnotes.)