This study was an attempt to integrate cognitive development (i.e., cognitive control) and emotional development (i.e., emotion regulation) in the first years of life. The construct of temperament was used to unify cognition and emotion because of its focus on attentional and regulatory behaviors. Children were seen at 8 months and 4 1/2-years of age in a study designed to examine the correlates of working memory development. Frontal brain electrical activity and temperament predicted working memory performance at 8 months. Similarly, frontal brain electrical activity, temperament, and language predicted working memory at age 4 1/2-years. Temperament in early childhood mediated the relation between infant temperament and early childhood working memory performance. These associated temperament characteristics highlight the value of early-learned regulatory and attentional behaviors and the impact of these early skills on later development.