Nadi shodhana, purification of the channels, is the alternate nostril breathing technique of the hatha yoga tradition, in which the practitioner closes one nostril at a time using the fingers in a fixed pattern to inhale and exhale alternately through each side, a practice classical hatha texts describe as clearing and balancing the nadis, the network of subtle channels through which prana, vital breath or energy, is understood to circulate through the body in the tradition's own physiological model.
The Hatha Yoga Pradipika, one of the foundational medieval texts of the hatha yoga tradition, includes nadi shodhana among its treatment of pranayama, breath discipline, describing the practice as preparatory purification necessary before more advanced pranayama and meditative work can be undertaken safely and effectively, positioning it as a foundational rather than advanced technique within the classical curriculum even though its correct performance still requires real attentiveness and instruction. The specific pattern of alternation, and the ratios of breath length classical texts sometimes specify between inhalation, retention and exhalation, vary somewhat between different hatha yoga lineages and later teaching traditions, reflecting the general pattern across pranayama practice of a shared core technique elaborated somewhat differently by different teaching lines.