Antonius H. N. Cillessen, PhD, is Professor and Chair of Developmental Psychology in the Behavioural Science Institute and Vice Dean of the Faculty of Social Science at Radboud University in Nijmegen, The Netherlands. Dr. Cillessen’s research interests include peer relationships in childhood and adolescence, popularity, aggression and antisocial behavior, the development of social cognition, and research methods for developmental psychology (sociometric methods, social network analysis, observational research, and longitudinal design and analysis). He has served on the editorial boards of Developmental Psychology, the Merrill-Palmer Quarterly, and the International Journal of Behavioral Development. David Schwartz, PhD, is Associate Professor in the Department of Psychology at the University of Southern California in Los Angeles. Dr. Schwartz’s research is broadly concerned with the links between social problems in the peer group during childhood and adolescence and the development of psychopathology. He has published widely on topics related to bully/victim problems in school peer groups, community violence exposure, peer relationships across cultural contexts, friendship, aggression, and popularity. Dr. Schwartz has also served on the editorial boards of Child Development, Developmental Psychology, and the Journal of Abnormal Child Psychology. Lara Mayeux, PhD, is Associate Professor in the Department of Psychology at the University of Oklahoma in Norman. Dr. Mayeux’s primary research interests are peer relationships and the development of peer status in middle childhood and adolescence, with a particular focus on popularity. Her work, funded by the National Science Foundation, has focused on behavioral, social-cognitive, and gender issues in popularity.