The present study evaluated moderators and processes of change in a randomized controlled trial comparing exposure and response prevention (ERP) delivered from a traditional framework versus ERP from an acceptance and commitment therapy framework (ACT+ERP) for obsessive-compulsive disorder (OCD). This paper presents baseline, weekly session, posttreatment, and follow-up data from the study. We examined (a) moderation effects of anxiety, depression, psychological inflexibility, and interpretation of intrusions and (b) the role of psychological inflexibility and interpretation of intrusions respectively as processes of change. Participants with less dysfunctional appraisals at pretreatment performed consistently better in ERP relative to ACT+ERP. In process analyses, psychological inflexibility and interpretation of intrusions positively influenced OCD severity over time in both conditions but OCD symptom severity also positively influenced psychological inflexibility and interpretation of intrusions in both conditions. Furthermore, whereas OCD symptom severity strongly and positively predicted dysfunctional appraisals over the course of treatment in ERP, symptom severity had a weaker positive effect on dysfunctional appraisals in ACT+ERP. Clinical and theoretical implications as well as study limitations are discussed.