The Upanishads are the most sacred texts of the Hindu religion,
considered to contain the ultimate truth and the knowledge that leads to
spiritual emancipation. They are the finest examples of Indian
metaphysical and speculative thought. Out of the traditional 109
Upanishads, ten of them are considered to be the principal ones: Isha,
Kena and Katha, Prashan, Mundaka, Mandukya, Tattiriya, Aitareya,
Chhandogya and Brihadaranyaka. The Ten Principal Upanishads is an
introduction of the primary Upanishads to the uninitiated.