This introduction summarizes the articles in this collection. It describes how the articles address one or more of the key elements of the child care research model: (a) selecting and measuring the independent variablesto determine the characteristics ("qualities") of the child care environment (and, in some studies, the characteristics of parents and family), (b) selecting and measuring the dependent variablesto determine the child's physical and developmental status after a period of time in a particular child care arrangement (usually a school year) compared with that of children in other arrangements (or simply the same child before spending time in the arrangement), (c) establishing causal linksbetween the independent and dependent variables that are either assumed in randomized experiments or estimated through statistical controls in nonexperimental studies, and (d) assessing impacts across subgroups to see whether the program benefits one particular group more (or less) than others. The collection closes with a proposal to develop a systematic federal research program to pursue improvements in child care and early childhood education programs.