Kriya Yoga is described by its practitioners as the ancient Yoga system revived in modern times, brought to international awareness by Yogananda's book Autobiography of a Yogi and through Yogananda's introductions of the practice to the West in the 1920's. Dynamic, yet meditative asana flows that include the subtle aspects of yoga : mantra (chanting and recitation of spiritual scriptures), mudra and bandha (teachings/transmission). The Kriya yoga system consists of a number of levels of pranayama, mantra, and mudra based on techniques intended to rapidly accelerate spiritual development and engender a profound state of tranquility and God-communion.