The role that exposure plays and the related mechanisms of actions that contribute to the successful treatment of arachnophobia by cognitive behavioral therapy (CBT) versus acceptance and commitment therapy (ACT) were explored using a multiple baseline across participants single-subject design. Both interventions produced equivalent statistically and clinically significant improvements for nine arachnophobic participants that were maintained through 2 months of follow-up and moderated by lower levels of pretreatment experiential avoidance. Analyses of both macro- and microlevel process measures suggested that the two approaches instigated therapeutic change through mechanisms consistent with the different conceptual models on which each is based. Specifically, at a macrolevel, while greater anticipated reductions in spider-related beliefs were not obtained for CBT, increased levels of willingness for further contact with spiders, as expected, were reported by ACT participants. At a more microlevel of analysis, CBT alone, as hypothesized, produced significant decrements in measures of subjective fear and disgust with only reductions in fear mediating increased approach behavior towards the spider. Limitations of this study and implications of its findings for future research and clinical management of exposure-based approaches to the treatment of anxiety disorders, more generally, and of arachnophobia and other types of specific phobia, in particular, are discussed.