Ānāpānasati (Pali; Sanskrit ānāpānasmṛti), meaning "mindfulness of breathing" ("sati" means mindfulness; "ānāpāna" refers to inhalation and exhalation), paying attention to the breath. It is the quintessential form of Buddhist meditation, attributed to Gautama Buddha, and described in several suttas, most notably the Ānāpānasati Sutta (MN 118).
Derivations of anāpānasati are common to Tibetan, Zen, Tiantai, and Theravada Buddhism as well as Western-based mindfulness programs.
The Ānāpānasati Sutta prescribes mindfulness of inhalation and exhalation as an element of mindfulness of the body, and recommends the practice of mindfulness of breathing as a means of cultivating the seven factors of awakening, which is an alternative formulation or description of the process of dhyana: sati (mindfulness), dhamma vicaya (analysis), viriya (persistence), pīti (rapture), passaddhi (serenity), samadhi (unification of mind), and upekkhā (equanimity). According to this and other sutras, the development of these factors leads to release (Pali: vimutti; Sanskrit mokṣa) from dukkha (suffering) and the attainment of nirvana.
Derivations of anāpānasati are a core meditation practice in Theravada, Tiantai, and Chan traditions of Buddhism as well as a part of many mindfulness programs. According to Anālayo, in both ancient and modern times anāpānasati by itself is likely the most widely used Buddhist method for contemplating bodily phenomena.
Satipatthana Sutta
The mindfulness practice described in the Ānāpānasati Sutra is to go into the forest and sit beneath a tree and then to simply watch the breath:
Breathing in long, he discerns, 'I am breathing in long'; or breathing out long, he discerns, 'I am breathing out long.' Or breathing in short, he discerns, 'I am breathing in short'; or breathing out short, he discerns, 'I am breathing out short.' He trains himself, 'I will breathe in sensitive to the entire body.' He trains himself, 'I will breathe out sensitive to the entire body.' He trains himself, 'I will breathe in calming bodily fabrication.