<P> More than 200 Upanishads are known , of which the first dozen or so are the oldest and most important and are referred to as the principal or main ( mukhya ) Upanishads . The mukhya Upanishads are found mostly in the concluding part of the Brahmanas and Aranyakas and were , for centuries , memorized by each generation and passed down orally . The early Upanishads all predate the Common Era , five of them in all likelihood pre-Buddhist ( 6th century BCE ) , down to the Maurya period . Of the remainder , 95 Upanishads are part of the Muktika canon , composed from about the last centuries of 1st - millennium BCE through about 15th - century CE . New Upanishads , beyond the 108 in the Muktika canon , continued to be composed through the early modern and modern era , though often dealing with subjects which are unconnected to the Vedas . </P>
the teachings of the upanishads were passed along in the form of
memorized by each generation and passed down orally