Through her theoretical and empirical work, Mary Rothbart has had a profound impact on the scientific understanding of infant and child temperament. This special issue honors her contributions through the presentations of original, contemporary studies relevant to three primary themes in Rothbart's conceptual approach: the expansive scope and empirically-derived structure of temperament, the importance of considering developmental change, and the interplay of reactive and regulatory processes. In addition to summarizing these themes, this introductory article acknowledges the ways Mary has spurred progress in the field through methodological advances, institutional service, and pedagogy.