Chandogya Upanishad is one of the oldest Upanishads
and comes under the
. It is the last eight chapters of Chandogya Brahmana.
Chandogya Upanishad has eight sections and the first five deals with various Upasanas or forms of approaching the ideal and the last three explains the way of attaining true knowledge. Chandogya Upanishad highlights the importance of chanting the sacred Om or Aum. It also advises to lead a religious life, with sacrifice, austerity, charity, and the study of the
Vedas. The doctrine of reincarnation appears in this Upanishad.