The epidemiology of traumatic experiences in childhood is a key context for research, clinical treatment, program management, and policy development. The conceptual, methodological and programmatic challenges in precisely answering even relatively simple questions concerning the basic prevalence and incidence of important trauma types among American youth are discussed. Findings from studies employing nationally representative samples and directly interviewing youth about their trauma histories are reviewed. Lifetime prevalence rates are presented for 1) sexual victimization, 2) physical abuse and assault, 3) witnessing violence in the home and the community, 4) traumatic death of a loved one, 5) internet-assisted victimization, 6) exposure to natural or man-made disasters, 6) motor vehicle accidents, and 7) other accidents. Clinical application of this information and future directions are discussed.