Upanishads

Upanishads, Hindu esoteric and mystical writings grouped in the Aranyakas, which are part of the Veda. The philosophical concepts contained in the Upanishads served as the basis of one of the six orthodox systems of Hindu philosophy, Vedanta. Some 150 Upanishads exist (108, according to the traditionally accepted number). Most are written in prose with interspersed poetry, but some are entirely in verse. Their lengths vary: The shortest can fit on 1 printed page, while the longest is more than 50 pages. They are believed to have been composed between the 8th century BC and the 5th century BC.

The underlying concern of the Upanishads is the nature of Brahman, the universal soul; and the fundamental doctrine expounded is the identity of atman, or the innermost soul of each individual, with Brahman. Formulations of this doctrinal truth are stressed throughout the Upanishadic writings. Other topics include the nature and purpose of existence, various ways of meditation and worship, eschatology, salvation, and the theory of the transmigration of souls.