One of the most frequent requests I receive from graduate students is for references on how to formulate a complex clinical case. Typically, after reading the recommended materials, the student returns to request more detailed accounts of how clinicians "think" about particular cases. The general lack of such materials in the behavior therapy Iiterature led to the formation of the present volume. Throughout much of the behavior therapy literature, one gets the impression that most cases seen present circumscribed and straight fmward psychological problems. In my experience, such cases are rare. Accordingly, the present volume was designed to cover more complex problemssuch as sociopathy and paranoid personality. Thesedisorders are rarely discussed in the behavior therapy Iiterature but nonetheless seem to appear regularly in clinical settings. The cases presented in this book are descriptions of patients seen clinically by the editor or by the contributors. Work an this text began while I was a faculty member at Vanderbilt University and took several years to complete. As the contributors would attest, the task I set out for them was atypical and often difficult. The complexities involved in articulating how one conceptualizes a case are numerous and may help to explain why there are so few sources available on case formulation. The fact that our current state of knowl edge in psychopathology is rather limited further exacerbates the problem.