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.