This chapter reviews the historical context regarding the development and evolution of cognitive processing therapy (CPT) for post-traumatic stress disorder (PTSD) over the years. We briefly discuss the theoretical background that influenced the development of the therapy and provide an overview of the course of treatment. Additionally, we review the various iterations of the therapy, from the original treatment developed by Resick and Schnicke to the most recent version of the comprehensive therapist manual, including changes to the treatment over time. Finally, we provide an overview of the clinical and psychosocial complexities associated with PTSD and highlight how each section of the book will illustrate how these factors can be addressed within the context of CPT.