Today, much of the field of psychology has accepted mindfulness as a choice of intervention, and most practitioners and researchers have applauded its effectiveness in mental health practices. However, there are emerging criticisms from spiritually-sensitive clinicians on this application of mindfulness; they argue that the current practice of western mindfulness has employed a reductionistic approach, extracting the mindfulness component from Buddhism and modifying it in a secular way for clients. A number of scholars have recommended that practitioners and researchers acquire a foundation in Buddhist teachings and an understanding of the Buddhist rationale for mindfulness to effectively and ethically incorporate mindfulness as a treatment component. In response to that recommendation, this article aims to explain the Buddhist assumptions, rationales, and practices of mindfulness from a psychological perspective. In particular, it uses original Buddhist scriptures, the actual practices of Buddhist monks, and real-life examples to explain the construct of Buddhist mindfulness in order to increase understanding of Buddhist mindfulness among mental health professionals.