Yoga Tattwa Upaniṣad is Volume 2 in the Yoga Upaniṣad series. Volume 1 is Yoga Chudamani, commentary by Swami Satyadharma, published by Yoga Publications Trust in 2003.
Yoga Tattwa Upaniṣad is an ancient treatise of 142 verses which deals with the philosophy, systems and practices of yoga. It is a significant integration of Vedānta and Tantra, expounding important topics such as mantra yoga, laya yoga, haṭha yoga, raja yoga, and the four stages of yoga. The text discusses particular practices of yoga: nāḍīśodhan prāṇāyāma, kumbhaka, bandhas, mahāvedha, khecarī mudra, viparītakaraṇī mudra, vajrolī mudra, and amarolī. It further discusses the five tattwas, or elements of creation: earth, water, fire, air and ether, and provides detailed instructions on how to meditate upon and realize these elements and their associated powers.
Included in the text are the original Sanskrit verses, transliteration, word meanings and translation by Ruth Perini, as well as a comprehensive commentary by Swami Satyadharma Saraswati.