We tested associations among empathic responsiveness, attachment style, and vagal tone (a physiologic index of emotion regulation) in 103 mother-adolescent dyads. Dyads discussed positive and negative topics and then separately reviewed a videotape of the interaction and rated their own and the other person's affect at one-minute intervals. We used multilevel modeling to analyze the association between one's rating of the other person's affect and the other person's affect (empathic sensitivity), and the association between one's rating of the other person's affect and one's own affect (perceived concordance). Adolescents' empathic responsiveness was predicted by attachment style, vagal tone, and interactions between them. Adolescents with the greatest empathic responsiveness had low levels of attachment insecurity and high levels of vagal tone.