Although trauma and its consequences are not new, the understanding of the mental, emotional, and physical symptoms that often follow traumatic events as a distinct disorder is relatively recent. The addition of posttraumatic stress disorder (PTSD) to the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) in 1980 had a large impact on theory, research, and treatment of the psychological consequences of trauma. Much of the early research focused on identification and assessment of symptomatic reactions to trauma and attempts to identify risk factors for the development of PTSD. Research on treatment of PTSD has emerged more recently and is still in the relatively early stages.Since the last edition of In Session on PTSD in 1997, there have been multiple advances in the treatment of PTSD. Most notable is research that has examined the efficacy of combined psychotherapy approaches in the treatment of PTSD and research that has compared the effectiveness of different treatments. Another area of growth has been the use of pharmacotherapy in the treatment of PTSD, especially the use of sertraline as an effective and well-tolerated treatment for PTSD. In the last few years, there also has been an increased interest among clinicians and researchers in eye-movement desensitization and reprocessing (EMDR) for patients with PTSD. The clinical significance of PTSD is reflected in the recent publications of experts' consensus statements on PTSD (e.g., Ballenger et al., 2000) and on practice guidelines for the treatment of PTSD (e.g., Foa, Keane, & Friedman, 2000). In the wake of the terrorist attacks on September 11, the effects of trauma have been featured prominently in the media and professional journals, and-hopefully-there will be a heightened importance of appropriate mental health care for trauma survivors.The purpose of this issue of In Session is to describe the theory and practice of the psychosocial approaches at the forefront in PTSD treatment, with plentiful case illustrations. The issue begins with an overview of clinically relevant research findings provided in the excellent article by Schnurr, Friedman, and Bernardy. With its summary of findings on the prevalence and course of PTSD, their article provides a context for understanding the importance of developing effective treatments. The discussion of the comorbidity associated with PTSD highlights one of the many complex issues in treatment in this area: PTSD symptoms rarely are found alone. More commonly, the diagnosis is associated with one or several comorbid disorders or associated features, complicating treatment decisions. Their summary of some of the exciting research advances in information processing and psychobiology illustrates the broadening of our knowledge of the mechanisms that may underlie the development and maintenance of PTSD symptoms, knowledge likely to be critical to future advances in prevention and treatment. The section on assessment provides a useful overview of relevant considerations for the practicing clinician, includ...