The field of traumatic stress has experienced significant growth in the number of psychotherapy treatment studies conducted, especially in the past 10 years. In this article, the author aims to help both the readers of this work and psychotherapy researchers by reviewing key concepts in trial design and discussing issues unique to psychotherapy (and other nonpharmacological interventions). The discussion is broad and nontechnical, particularly with respect to statistical issues. The focus is on between-group randomized designs, and on outcome rather than process. Examples are drawn from posttraumatic stress disorder treatment studies to enhance relevance to the field of traumatic stress.