The present volume contains the Text Translation, important Notes and exhaustive Commentaeyh on Nine Principal Upanishads. Originally, these Principal Texts in two volumes in earlier, and sometime aftr the publication of the same, these works of his Holiness Sri Swami Sivanandaji Mahaeraj went out of print for many years For some reason or other, the repeinting of these famous Scriptures of the commentary of his Holiness could not become possible, though students of the Prasthanatraya,-the triple foundation of Indina Philosophy, viz., the Upanishads, the Brahmasutras and the Bhagavadgita,- were eager to see the coming out of these treasures of writing and were actually communicating to us their requests in this regard incessantly.