The number of minor Upanishads varies from fifty to ninety eight (mentioned in Muktika Upanishad) and even more than two hundred. The Adyar Library has published all the 108 Upanishads. Some other minor Upanishads were published by Schrader under the heading Unpublished Upanishads (Adyar Library). The Ten Main Upanishads The 10 principal Upanishads are Isha Upanishad, Kena Upanishad, Katha Upanishad, Prashna Upanishad, Mundaka Upanishad, Mandukya Upanishad, Taittiriya Upanishad, Chandogya Upanishad, Aitareya Upanishad and Brihadaranyaka Upanishad. Adi Shankaracharya has written commentaries on them. The minor Upanishads find mention in Shankaracharya’s commentary on Upanishads. Svetasvatara Upanishad, Kaushtaki Upanishad, Maitri Upanishad and Nrisimha Tapaniya Upanishad are mentioned by Adi Shankaracharya but he has not written commentary on them. Six Volumes Of Minor Upanishads The six volumes of minor Upanishads, on the basis on the subject matter, which the Adyar Libr