Defusion and decentering are related constructs that describe an objective, distanced, and open approach toward one’s internal experiences. These constructs are thought to play important protective roles in models of psychopathology, and several common therapeutic interventions include techniques to increase levels of defusion and decentering. However, little research has examined the construct validity or the underlying structure of measures of these constructs. Across 4 samples—3 unselected student samples and 1 clinical sample— we examined 5 self-report measures of defusion/decentering. We found that measures of decentering and defusion were only weakly to modestly associated with each other. Item-level analyses revealed a 2-factor structure, consisting of “Observer Perspective” and “Reduced Struggle with Inner Experience,” which generally showed expected and distinct patterns of convergent and discriminant validity, although the latter factor had questionable discriminant validity namely a-namely indices of psychological distress (e.g., neuroticism, negative affect, internalizing symptoms, rumination). The factors also related differently to believability of positive versus negative thoughts, which was partially explained by the overrepresentation of negative items in the measures. Implications for the structure and validity of these constructs, as well as for their assessment and use in clinical settings, are discussed.