The clinical and empirical literature on trauma and loss in infancy and early childhood largely focuses on children's exposure to traumatic events, direct "event trauma." This article seeks to expand the definition of trauma in infancy to include "indirect trauma," implicit emotional and relational events, such as infant exposure to traumatized parents, which occurred in the Project for Mothers, Infants, and Young Children of September 11, 2001, described in this issue. Four empirical literatures are reviewed to develop an understanding of the cognitive, behavioral, and social sequelae of early trauma and parental loss: (1) research on childhood trauma symptoms in the verbal period; (2) research on child and parent attachment security and the parent-child relationship; (3) research on the preverbal period of infant development, specifically addressing nonverbal parent-child communication patterns; and (4) research on the impact of maternal trauma prenatally, on the infant's capacity to remember and represent trauma occurring preverbally, and on the effect of early trauma on neurological development. The article argues that trauma and treatment in infancy and early childhood should be construed as dyadic, occurring between parent and child.In response to traumatic events of the last decade, researchers and clinicians have struggled to define and treat exposure to trauma and loss in early childhood (