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.