Synopsis This edition of the Chandogya Upanisad is a companion volume to the translator’s Eight Upanisads published by us. Together with the monumental work on the Brhadaranyak Upanisad by Swami Madhavananda, which is also published by us, it brings to completion the English translation of the commentary of Sankaracarya on all the ten principal; Upanisads. We have already published he translator’s masterly English rendering of the Brahma-Sutra Bhasya of Sankaracarya. The English version of Sankara’s commentary on the Bhagavad-Gita, now under preparation by him and to be published by us in due course, will complete the prasthana-traya (the three source-books) of the Vedanta darshana from the Advaita point of view and fulfil a long-felt need in this respect. The Chandogya Upanisad forms the lat eight chapters of the Chandogya Brahmanaya of the Sama-Veda. It is the second biggest of the major Upanisads, next only to the Brhadaranyaka. It seems to have been an important source-book for the author of the Brahma-Sutras, as he makes copious references to its numerous topics, which may be as manyas one hundred and thirty according to some scholars. Sankaracarya also held this Upanisad in great esteem. He has cited profusely from it in his bhasya on the Brahma-Sutras.  This Upanisad introduces us to such endearing and earnest seekers after truth as Narada, Satyakama, and Svetaketu, as well as such sagely and compassionate teachers as Aruni, Sanatkumara, and Prajapati.