Recent research suggests that many preschoolers routinely experience unstable child care, which refers to children's consistency in experience with care providers or in care arrangements. Other research shows these unstable care experiences have negative effects on children's school readiness and adjustment outcomes. The current study looks at this important area of research in child care and specifically examines the effects of several types of child care stability-including frequency of child care arrangement and caregiver changes, use of multiple concurrent child care arrangements over time, and staff turnover rates in center-based child care-on children's school readiness and adjustment outcomes, the rates and effects of child care stability on children from families of varying income levels, and the mediating influences of two potential processes-child-caregiver attachment relationships and the child care quality-on children's school readiness and adjustment outcomes. The implications of the study findings and future directions of the research are discussed.