© 2017, Association for Behavior Analysis International. Acceptance and commitment therapy (ACT) is a contextual–behavioral approach to psychotherapy and other behavioral health concerns that has progressively attracted attention from both researchers and clinicians. ACT’s psychological flexibility model relies on middle-level terms that, despite being less precise than behavioral principles, are seen as being valuable for teaching and practicing ACT. One such term is cognitive defusion, which refers to the reduction of stimulus function transformation that occurs through verbal relations. In other words, defusion aims to minimize the influence of verbal relations, such as thoughts, on behavior, when doing so leads to adaptive behavior and valued living. Recently, some authors have stressed the importance of functionally defining middle-level terms, establishing clear links between the concept and basic behavioral processes. This article begins this endeavor by analyzing these links with respect to cognitive defusion. First, we briefly contextualize ACT’s theoretical roots. Second, we present cognitive defusion as a therapeutic intervention, reviewing its objectives, procedures, outcomes, and hypothesized processes as stated in the relevant literature. Third, the outlined process of change is critically examined, leading to a new conceptualization of cognitive defusion. Finally, the conceptual, clinical, and research implications of this new conceptualization are considered.