Kriya Yoga is described by its practitioners as the ancient Yoga system revived in modern times by Mahavatar Babaji through his disciple Lahiri Mahasaya, c. 1861. To Westerners, it was brought into popular awareness through Paramahansa Yogananda's book Autobiography of a Yogi and through Yogananda's introductions of the practice in the west since 1920 and India since 1917. The system consists of a number of levels of Pranayama based on techniques that are intended to rapidly accelerate spiritual development and engender a profound state of tranquility and God-communion.
In the ancient text on yoga called the Yoga Sutras of Patanjali, Patanjali gives a description of Kriya Yoga in the second chapter. Yogananda wrote that Patanjali refers to the Kriya technique when he wrote in the Yoga Sutras II:49: "Liberation can be attained by that pranayama which is accomplished by disjoining the course of inspiration and expiration.