In a review written in 1979, I noted that there was a paucity of research examining the effects of maternal employment on the infant and young child and also that longitudinal studies of the effects of maternal em ployment were needed (Hoffman, 1979). In the last 10 years, there has been a flurry of research activity focused on the mother's employment during the child's early years, and much of this work has been longi tudinal. All of the studies reported in this volume are at least short-term longitudinal studies, and most of them examine the effects of maternal employment during the early years. The increased focus on maternal employment during infancy is not a response to the mandate of that review but rather reflects the new employment patterns in the United States. In March 1985, the Bureau of Labor Statistics reported that 49.4% of married women with children less than a year old were employed outside the home (Hayghe, 1986). This figure is up from 39% in 1980 and more than double the rate in 1970. By now, most mothers of children under 3 are in the labor force.