Mindfulness has been widely disseminated in clinical psychology in recent years, due to the positive effects on treating several psychological issues in diverse population. Nonetheless, empirical research and theoretical reviews show three different meanings of mindfulness within behavioral approaches: as a process, as skill, and as a strategy. Discrepancies about mindfulness definitions have brought ambiguity to what and how this phenomenon is studied. A conceptual analysis of mindfulness according to behavioral-analytic and functionalcontextualistic philosophical traditions is presented. Finally, it was discussed the relevance of employing a precise and consensual definition of mindfulness to develop a coordinated research agenda in this field. Clinical psychology has shown a growing interest in mindfulness, given the positive effect of this intervention in different types of disorders and psychological problems, such as: mood disorder, binge eating disorder, anxiety and stress