Over the past two decades, scientific research on mindfulness has taken on unprecedented proportions, exponentially multiplying its fields of application and the number of publications. In a historical context in which the development of mindfulness in North America consistently takes place on the border between the spiritual and the secular, this article questions the modes of engagement employed by psychology researchers regarding the subject of mindfulness. In examining the social, moral and epistemological approaches at work in this science of mindfulness, analysis shows that it is intersected by tension between scientific justification and moral acceptance. This emerges via discourse that promotes, on the one hand, the scientific record as a register of justification and, on the other hand, the consideration of the existential, experiential and moral nature of mindfulness practices.