In American criminal law, if a defendant demonstrates that they lack certain psychological capabilities, they may be excused of blame and punishment for wrongdoing. However, criminal defense law often fails to consider the developmental science of individual differences in ability and functioning that may inform jurisprudential issues of rational capacity and responsibility in criminal law. This book discusses the excusing nature of a range of both traditional and non-traditional criminal law defenses and questions the structure of these defenses based on scientific findings from social and developmental psychology. This book explores how research on individual differences in the development of social perception, judgment and decision making explain why some youths and adults develop psychological tendencies that favor criminal behavior, and considers how developmental science can guide the understanding of criminal excuses and affirmative defense law.