Child care instability affects children’s development, parents’ employment, and family stability. This report describes why it matters, discusses definitional and measurement challenges, provides a framework to examine links between instability in child care and family domains, and examines the causes of instability (including child care subsidy policy and practice). Findings suggest that policies supporting stability in child care could interrupt the cascading effect of instability in other domains. Policy strategies to improve the Child Care and Development Fund/Child Care and Development Block Grant, such as funding, voucher flexibility, eligibility, quality of care, and referral systems, are examined.