Susan D. Calkins, PhD, is professor of human development, family studies, and psychology at the University of North Carolina at Greensboro, where she directs the Child and Family Research Network. She conducts longitudinal research, funded by the National Institute of Mental Health (NIMH), the National Institute of Child Health and Human Development, and the National Science Foundation on the development of biological and behavioral indicators of self-regulation across infancy, childhood, and adolescence. She is a fellow of American Psychological Association Division 7 (Developmental Psychology), a recipient of an NIMH Research Scientist Career Development Award, and an associate editor of the journal Developmental Psychology.   Martha Ann Bell, PhD, is associate professor of psychology at Virginia Polytechnic Institute and State University, Blacksburg. Her research specialization is developmental cognitive neuroscience, and she examines developmental change in frontal lobe functioning using both behavioral and electrophysiological methods. Her current work, funded by the National Institutes of Health and the National Institute of Child Health and Human Development, focuses on individual differences in the development of executive function and emotion regulation across infancy and early childhood. Dr. Bell is a fellow of American Psychological Association Division 7 (Developmental Psychology) and the editor of the journal Infancy.