With increased numbers of women employed in their children’s first year of life and with increased attention being paid by parents and policy makers to the importance of early experiences for children, establishing the links that might exist between early maternal employment and child cognitive outcomes is more important than ever. Negative associations between maternal employment during the first year of life and children’s cognitive outcomes at age 3 (and later ages) have been reported using data from the National Longitudinal Survey of Youth–Child Supplement. However, it was not known whether these findings would be replicated in another study, nor whether these results were due to features of child care (e.g., quality, type), home environment (e.g., provision of learning), and/or parenting (e.g., sensitivity). This study explored these issues using data on 900 European American children from the National Institute of Child Health and Human Development Study of Early Child Care, which provides information on child cognitive scores at 15, 24, and 36 months, as well as data about the home environment (as assessed by the Home Observation of the Measurement of the Environment Scale), parental sensitivity, and child–care quality and type over the first 3 years of life. Maternal employment by the ninth month was found to be linked to lower Bracken School Readiness scores at 36 months, with the effects more pronounced when mothers were working 30 hr or more per week and with effects more pronounced for certain subgroups (i.e., children whose mothers were not sensitive, boys, and children with married parents). Although quality of child care, home environment, and maternal sensitivity also mattered, the negative effects of working 30 hr or more per week in the first 9 months were still found, even when controlling for child–care quality, the quality of the home environment, and maternal sensitivity. Implications for policy are also discussed.