Dominic Abrams is Professor of Social Psychology and Director of the Centre for the Study of Group Processes at the University of Kent at Canterbury. His research expertise includes social identity and intergroup relations (e.g., the contact hypothesis, nationalism, collective protest, contemporary aspects of prejudice), deviance (particularly the subjective group dynamics model) and social identity in organizational contexts. He is the President of the Society for the Psychological Study of Social Issues, co-editor of Group Processes and Intergroup Relations, and co-editor of The Social Psychology of Inclusion and Exclusion (2005) with M.A. Hogg and J. M. Marques.Melanie Killen is Professor of Human Development and Quantitative Methodology, Professor of Psychology (Affiliate), and the Associate Director for the Center for Children, Relationships, and Culture at the University of Maryland. Her research expertise includes the development of social inclusion and exclusion, moral reasoning, intergroup attitudes, prejudice, and bias in peer groups, peer interactions and social relationships in childhood and adolescence. She is Associate Editor of the journal Child Development, co-author of Children and Social Exclusion: Morality, Prejudice and Group Identity (2011) with Adam Rutland, and Editor of the Handbook on Moral Development (2006, 2014) with Judith Smetana.