Brhadaranyaka Upanishad is the oldest and the most important of all the Upanishads
. Brhadaranyaka belongs to the Satapatha Brahmana and is ascribed to
Having derived its (Brhadaranyaka) name from great forest-book, it includes three kandas or sections, namely, Madhu Kanda, Muni Kanda (or Yajnavalkya Kanda) and Khila Kanda. The Madhu Kanda explains the teachings of the basic identity of the individual and the Universal Self. Muni Kanda includes the conversations between the sage Yajnavalkya, the great Upanishad philosopher, and his wife, Maitreyi. Various methods of worship and meditation are dealt in the Khila Kanda.
The doctrine of “Neti, Neti” (“not this, not this”) is found in this Upanishad.