The Cluster C personality disorders (obsessive-compulsive, avoidant, and dependent) are the most prevalent personality disorders (PDs) in outpatient samples. These PDs are highly comorbid with mood and anxiety disorders. Patients with comorbid PD and Axis I disorders present with more severe and chronic symptom profiles, and they do not respond well to psychotherapy or pharmacotherapy. It is particularly difficult to establish a therapeutic alliance, a well-documented predictor of treatment outcome, and treatment retention and compliance are often compromised. Given the prevalence of Cluster C PDs and their significant impact on psychosocial functioning, treatment response, and health care utilization, it is surprising that little attention has been paid to treatment development for this population. Cognitive therapy has been demonstrated to be an effective treatment across a number of Axis I disorders and recently has been extended to PDs. In a sample of patients with obsessive-compulsive (OCPD) and avoidant (AVPD) PDs, the first open trial of cognitive therapy for PDs (CT-PD) demonstrated significant improvements in personality symptoms, as well as in symptoms of depression and anxiety. Because the therapy is in early stages of development, general principles and guidelines for treatment of PDs are provided, but there are few specific details on how to treat OCPD and AVPD. This lack of specificity limits the extent to which the manual can be used to conduct larger scale clinical trials outside of the Center for Cognitive Therapy, where the manual was developed. The goal of this R-21 treatment development research is to identify active ingredients of the therapy and to use this process research to improve the specificity of the manual. CT-PD is thought to have its effects by exposing patients to corrective information challenging existing personality patterns, identifying the historical roots of these patterns, and providing exercises to facilitate generalization. The proposed study will examine these interventions as predictors of three hypothesized precursors of change: turbulence in defensiveness and avoidance (protection), the therapeutic alliance, and in-session affect. Growth curve modeling will be used to examine sequencing and timing of therapist interventions and relations between these interventions and the hypothesized precursors of change, which will then be examined as predictors of symptom reduction. Quality of therapeutic alliance in early sessions will be examined as a predictor of treatment retention. With this information, sections of the treatment manual on OCPD and AVPD can be refined, strategies to facilitate therapeutic alliance and symptom change can be specified, and the refined manual can be used in future proposals examining treatment efficacy.