Hypothesized Mechanisms of Change in Cognitive Therapy for Borderline Personality Disorder  Amy Wenzel, Jason E. Chapman, Cory F. Newman, Aaron T. Beck, and Gregory K. Brown University of Pennsylvania Preliminary evidence suggests that cognitive therapy (CT) is effective in treating borderline personality disorder (BPD). According to cognitive theory, BPD patients are characterized by dysfunctional beliefs that are relatively enduring and inflexible and that lead to cognitive distortions such as dichotomous thinking. When these beliefs are activated, they lead to extreme emotional and behavioral reactions, which provide additional con- firmation for the beliefs. It is hypothesized that a change in dysfunctional beliefs is the primary mechanism of change associated with CT. How- ever, additional mechanisms of change are likely also at work in CT, includ- ing enhancement of skills, reduction in hopelessness, and improvement in attitude toward treatment. Each of these mechanisms is discussed in light of cognitive theory, data from an open clinical CT trial, relevant lit- erature, and therapeutic interventions. Findings from the CT trial support the role of cognitive change during therapy and its continuation after termination. © 2006 Wiley Periodicals, Inc. J Clin Psychol 62: 503– 516, 2006. Keywords: borderline personality disorder; cognitive therapy; cognitive theory; dysfunctional beliefs A salient feature of patients who have borderline personality disorder (BPD) is their tendency to engage in dichotomous thinking, as they often evaluate themselves, other people, and their environment in extreme terms and demonstrate little flexibility in assim- ilating new information to modify their rigid beliefs (e.g., Arntz, 1994; Veen & Arntz, 2000). This pattern of distorted perception often results in angry outbursts, impulsive behavior, and /or severe and sudden symptoms of anxiety and depression. One purpose of cognitive therapy (CT) is to help patients develop tools to identify and evaluate such cognitive distortions, given that a realistic appraisal of one’s circumstances will reduce Correspondence concerning this article should be addressed to: Aaron T. Beck, M.D., Psychopathology Research Unit, Department of Psychiatry, University of Pennsylvania, 3535 Market St., Room 2032, Philadelphia, PA 19103; e-mail: abeck@mail.med.upenn.edu. JOURNAL OF CLINICAL PSYCHOLOGY, Vol. 62(4), 503–516 (2006) © 2006 Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jclp.20244