| 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.<ref name="stephenphillips">Stephen Phillips (2009), Yoga, Karma, and Rebirth: A Brief History and Philosophy, Columbia University Press, ISBN 978-0231144858, Chapter 1</ref><ref>E Easwaran (2007), The Upanishads, ISBN 978-1586380212, pages 298-299</ref> The ''mukhya'' Upanishads are found mostly in the concluding part of the ''[[Brahmanas]]'' and ''[[Aranyakas]]''{{sfn|Mahadevan|1956|p=56}} and were, for centuries, memorized by each generation and passed down [[oral tradition|verbally]]. The most important Upanishads are Isa, Kena, Katha, Prasna, Mundaka, Mandukya, Aitareya, Taittiriya, Chhandogya, Brihadaranyaka, Kaushitaki, Svetasvatara and Maitrayani. | | 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.<ref name="stephenphillips">Stephen Phillips (2009), Yoga, Karma, and Rebirth: A Brief History and Philosophy, Columbia University Press, ISBN 978-0231144858, Chapter 1</ref><ref>E Easwaran (2007), The Upanishads, ISBN 978-1586380212, pages 298-299</ref> The ''mukhya'' Upanishads are found mostly in the concluding part of the ''[[Brahmanas]]'' and ''[[Aranyakas]]''{{sfn|Mahadevan|1956|p=56}} and were, for centuries, memorized by each generation and passed down [[oral tradition|verbally]]. The most important Upanishads are Isa, Kena, Katha, Prasna, Mundaka, Mandukya, Aitareya, Taittiriya, Chhandogya, Brihadaranyaka, Kaushitaki, Svetasvatara and Maitrayani. |