Pranayama or breath-control,  a variety of breathing-techniques, occupies a very important place in the science of Yoga. According to it there is an astral body besides the physical body, and the entire Yoga-System consisting of Shat-Karma, Asanas and Pranayama gives full control over both, which is the essential requirement for spiritual development. Breath control has three phases, namely inhalation (Puraka), breath-retention (Kumbhaka) and exhalation (Recaka). Pranayama is the main technique for the cleansing and activation of nerves and Nadis, a network of subtle channels carrying the life-force Prana, and is one of the chief means of rejuvenating the body and calming and controlling the movement of the mind. Mastering Prana helps the Yogi to awaken Kundalini and to reach the abode of unending bliss. A man practicing Yoga without attempting the control of the breath is compared to a person who wants to cross the ocean in an unbaked earthen vessel, which is bound for failure.
The Yoga-Shastra mentions ten kinds of Kumbhakas which are of special importance: Nadishodhana-Pranayama (Purification of Nadis), Surya-Bhedi or Surya-Bhedana (piercing of the sun), Ujjayi (victorious), Sitkari & Shitali (cooling), Bhastra-Kumbhaka (bellows-kumbhaka), Bhramari (bee-humming), Murccha (swooning), and Plavini (floating). Kevala-Kumbhaka, the absolute retention of breath, is the highest form of Pranayama and the key for entering the realms of deep meditation.Before Pranayama can be started without danger, the aspirant must engage various purificatory practices (Sukshma-Vyayama and Shat-Karma), mastery of postures (Asana) and a moderate diet (Mitahara). Upon mastery of Pranayama, the Yogi is fit to proceed to the higher stages of meditation and Raja-Yoga.
The “Hathayoga-Pradipika” advises caution in performing breath-control: “Just as a lion, an elephant or a tiger is tamed gradually, so should the life-force be controlled; else it will kill the practitioner.”