Many philosophers endorse the Transparency Thesis, the claim that by introspection one cannot become aware of one's experience. Recently, some authors have suggested that the Transparency Thesis is challenged by introspective states reached under mindfulness. We label this the Mindfulness Opacity Hypothesis. The present paper develops the hypothesis in important new ways. First, we motivate the hypothesis by drawing on recent clinical psychology and cognitive science of mindfulness. Secondly, we develop the hypothesis by describing the implied shift in experiential perspective, (...) the scope of introspectable qualities, and the level of skill. Thirdly, we defend the hypothesis against various philosophical arguments. We conclude that the Mindfulness Opacity Hypothesis is empirically and theoretically well motivated and supported. (shrink)