This article provides a review and synthesis of concepts, research programs, and measures in the infant and child temperament area. First, the authors present an overview of five classical approaches to the study of child temperament that continue to stimulate research today. Subsequently, the authors carve out key definitional criteria for temperament (i.e., inclusion criteria) and the traits that qualify as temperamental according to the overview and defined criteria. The article then reviews leading programs of research that are concerned with the ways in which early childhood temperament affects psychosocial development, both normal and abnormal. After touching on measurement issues and tools, the authors conclude with an outlook on child temperament research.