Brihadaranyaka Upanishad is one of the oldest Upanishads and often referred to as the greatest both in substance, length, and theme. It is estimated that Brihadaranyaka Upanishad was compiled about 2.700 years ago from much older, now lost, material. Brihadaranyaka Upanishad means “Upanishad of the great forests” and it centers around the fundamentals of the Atman, Soul, or Self.
It is in the Brihadaranyaka Upanishad we first see the written conceptualization of Karma and non-duality and other foundations for Hinduism and Buddhism. The work consists of six chapters dealing with such comprehensive themes as the Vedic theories of the creation of the Universe to metaphysical, spiritual, and psychological matters.