Ānāpāna-sati: Awareness or mindfulness on & by in-and-out-breathing, is one of the most important trainings for reaching mental concentration and the 4 absorptions jhāna. In the Satipatthāna Sutta M. 10, D. 22 and elsewhere, 4 methods of practice are given, which may also serve as basis for insight meditation. The speech on Awareness by Breathing’ Ānāpānasati Sutta, M. 118 and other texts have 16 methods of practice, which divide into 4 groups of four. The first three apply to both calm samatha and insight-meditation, while the fourth refers to pure insight praxis only. With attentive mind he breathes in, with attentive mind he breathes out.

I. First Tetrad:
1: When making a long inhalation he understands: I make a long inhalation; when making a long exhalation he understands: I make a long exhalation.

2: When making a short inhalation he understands: I make a short inhalation; when making a short exhalation he understands: I make a short exhalation.

3: Clearly perceiving the entire body I will breathe in, thus he trains himself; clearly perceiving the entire breath-body I will breathe out, thus he trains himself.

4: Calming all bodily activity I will breathe in, thus he trains himself; calming all bodily activity I will breathe out, thus he trains himself.

II. Second Tetrad:
5: Experiencing joy pīti I will breathe in, thus he trains himself; Experiencing joy I will breathe out, thus he trains himself.

6: Experiencing a pleasurable happiness I will breathe in, thus he trains himself; Experiencing a pleasurable happiness I will breathe out, thus he trains himself.

7: Experiencing the mental construction citta-sankhāra I will breathe in, thus he trains himself, Experiencing the mental construction I will breathe out, thus he trains himself.

8: Calming the mental construction I will breathe in, thus he trains himself; calming the mental construction I will breathe out, thus he trains himself.

III. Third Tetrad:
9: Experiencing the mind & mood citta I will breathe in, thus he trains himself; clearly perceiving the mind & mood I will breathe out, thus he trains himself.

10: Gladdening the mind I will breathe in, thus he trains himself; gladdening the mind I will breathe out, thus he trains himself.

11: Concentrating the mind I will breathe in, thus he trains himself; concentrating the mind I will breathe out, thus he trains himself.

12: Releasing the mind I will breathe in, thus he trains himself; releasing the mind I will breathe out, thus he trains himself

IV. Fourth Tetrad:
13: Reflecting on impermanence anicca I will breathe in, thus he trains himself; reflecting on impermanence I will breathe out, thus he trains himself.

14: Reflecting on disillusion virāga I will breathe in, thus he trains himself; reflecting on disillusion I will breathe out, thus he trains himself.

15: Reflecting on ceasing nirodha I will breathe in, thus he trains himself; reflecting on ceasing I will breathe out, thus he trains himself.

16: Reflecting on relinquishment patinissagga I will breathe in, thus he trains himself; reflecting on relinquishment I will breathe out, thus he trains himself.

In M 118 it is further shown how these 16 exercises bring about the 4 foundations of awareness satipatthāna, namely: 1-4 contemplation of the body, 5-8 contemplation of feeling, 9-12 contemplation of mind, 13-16 contemplation of mental states. Then it is shown how these 4 foundations of awareness or mindfulness bring about the 7 factors of enlightenment bojjhanga, and then how these again produce release of mind ceto-vimutti and release through understanding paññā-vimutti.

Literature: Ānāpānasati Samyutta see: LIV. - Pts.M. Ānāpānakathā - Full explanation of practice in Vis.M VIII, 145ff. - For a comprehensive anthology of canonical and commentarial texts, see: Mindfulness of Breathing, by Nānamoli Thera Kandy: BPS, 1964-98.