The major Upanishads were written between around 800 to 400 BC, and are a collection of texts which serve as interpretative summaries of the theologies of the original four Vedas. In fact, the Upanishads are also known as the Vedanta – the end of the Vedas – and are actually part of the Vedas, which all together constitute a part of the Shuti – the fundamentals of Hindu theology.
The Aitrayeya Upanishad and the Kaushitaki Upanishad belong to the Rig Veda; the Khandogya Upanishad and the Talavakara (Kena) Upanishad to the Samaveda; the Taittiriyaki Upanishad, the Katha Upanishad, the Svetasvatara Upanishad, the Brihadaranyaka Upanishad, and the Vagasaneyi (Isavashya) Upanishad to the Yashur Veda; and the Prasna Upanishad, the Mundaka Upanishad, and the Maitrayana-Brahmaya Upanishad to the Artharveda Veda.
There is no overall structure to the philosophies of the Upanishads, as each of which were developed by different sects under the authorship of a number of scribes, and instead many different themes are considered. Notable among them includes the unification of the human soul (Atman) to God (Brahma), through meditation and contemplation leading to self-realisation. They also expound upon the notion of karma.
The sage Yajnavalkya features in a number of Upanishads, and is held responsible for primary Hindu theologies, including some taken up through Buddhism – such as that of “neti-neti”, in which the universe is perceived as an illusionary projection of the self, and that Ultimate Truth can only be contemplated by the negation of active consciousness.
Traditionally, there are 108 primary Upanishads: the 12 mentioned above in connection with the Vedas; 23 Samanayayuvedanta Upanishads; 20 Yoga Upanishads; 17 Samnyasa Upanishads; 14 Vaisnava Upanishads; 14 Shaiva Upanishads; and 8 Shakta Upanishads. However, there are also believed to be hundreds of non-primary Upanishads.
Only the twelve major Upanishads are represented on this site.