Mandukya Upanishad

It analyses the entire range of human consciousness in the three states of waking (Jagrata), dream (svapna) and dreamless sleep (susupti) which are common to all men.It asserts unequivocally that the Absolute Reality is non-dual  (advaita) and attributeless (nirguna)

It has a unique method of approach to Truth. It provied symbol for meditation in the mono-syllable AUM comprising of three sounds A,U,M detailing its philosophical implications. According to Muktikopanishad, it forms the epitome of all the hundred and eight Upanishads which have been accepted as authentic.