The Upanishads are perhaps one of the oldest philosophical treatises concerned with the mystery of the Absolute. This work (in three volumes) presents a study of the twelve principal Upanishads , thus unfolding the spirit and substance of Upanishadic thought. Written in a lucid style, it offers the text of the Upanishads in Devanagari and its translation in English along with detailed noted incorporating the commentaries of prominent spiritual thinkers and teachers including Shankaracarya and Shankaranand. The authors, scholars who have put in years of intense study on the subject, here offer a fresh approach and new insights into the philosophy of absolute unity as taught by the Upanishads and its quest for answers to abstruse questions like the origin of the universe, the nature of deity and the soul, and connection of mind and matter. The volumes are a must for scholars of Indian philosophy as well as students, and especially those genuine aspirants who wish to achieve moksha by the process of yoga for moksha is not possible without understanding the meaning of the Upanishads.