Mindfulness (Sanskrit, smṛti; Pāli, sati) is a spiritual practice that is common to both early Buddhism and early Jainism. It plays a particularly important role in the former. Two conspicuously different forms of mindfulness are found near each other in the standard description of the path to liberation that occurs numerous times in the early canonical sermons: one in preparatory exercises and the other in meditation proper. During the former the (hypothetical) practitioner "acts consciously while going and while coming, while looking forward and while looking backward, while bending his limbs and while stretching them, while carrying his clothes and alms-bowl, while going, while standing, while sleeping, while waking, while speaking and while remaining silent." However, at some point the practitioner sits down, folds his legs, holds his body erect, and applies mindfulness. Applying mindfulness (Sanskrit, smṛtyupasthāna; Pāli, satipaṭṭhāna) is the precondition for the four stages of dhyāna (trance state) that follow. Indeed, mindfulness accompanies the practitioner in all of them, the fourth being characterized by "purity of equanimity and mindfulness." Clearly mindfulness in its highest degree of purity is required for the next step: reaching liberating insight.
As happens frequently in the Buddhist canon, a number of sermons present mindfulness itself or, more precisely, the applications of mindfulness as the way to liberation. Some of these sermons have smṛtyupasthāna or satipaṭṭhāna in their title, and distinguish four applications of mindfulness: (1) on the body; (2) on feelings; (3) on the mind; (4) on the dharmas. The Pāli Satipaṭṭhāna-sutta of the Majjhima Nikāya makes the highest promises to those who practice mindfulness: "If anyone should develop these four applications of mindfulness in such a way for seven days, one of two fruits could be expected for him: either final knowledge here and now, or if there is a trace of clinging left, non-return."
Mindfulness also figures in the noble eightfold path, at the seventh place, just before meditative concentration (samādhi). This position agrees with the account found in the standard description of the path to liberation, where mindfulness is a precondition for and an accompaniment of the four stages of dhyāna.
No doubt as a result of subsequent attempts to organize the received teachings of the Buddha, mindfulness came to be incorporated in various lists. It is, for example, the first of the seven "members of enlightenment" (bodhyaṅga). However, the list of seven members of enlightenment is itself an item in a longer list that altogether contains thirty-seven so-called aids to enlightenment (bodhipakṣyadharma). The artificial nature of this enumeration can be seen from the fact that this long list also, and separately, contains the four applications of mindfulness, plus mindfulness as included in the five faculties (indriya), in the five forces (bala), and in the noble eightfold path. That is to say, mindfulness by itself accounts for eight of the thirty-seven aids to enlightenment.
Bronkhorst, Johannes. "Dharma and Abhidharma." Bulletin of the School of Oriental and African Studies 48 (1985): 305–320.