Dialogue is mentioned in the Katha Upanishad (9th century BCE).

•   Chandogya Upanishad: It is an Upanishad of Samaveda. It is listed as No.9 in the Muktika canon of 108 Upanishads.

•   Mundaka Upanishad: it is an Upanishad of Atharvaveda. The words Satyameva Jayate have been taken from Mundaka Upanishad, meaning ‘Truth Alone Triumphs’. It is listed as No.5 in the Muktika canon of 108 Upanishads.

•   Katha Upanishad: It is an Upanishad of Yajurveda. It is listed as No.3 in the Muktika canon of 108 Upanishads.

•   Kena Upanishad: It is an Upanishad of Samaveda. It is listed as No.2 in the Muktika canon of 108 Upanishads.

•   It is the conversation between Nachiketa (The son of Sage Vajasravasa) and Yamraj (God of death).

•   Nachiketa was a seeker, and Yamraj was a Guru (knower of secrets).

•   Their conversation evolves to a discussion of the nature of man, knowledge, Atman (Self) and moksha (liberation).

•   It asserts that ‘Atman (Self) exists’, and it teaches that ‘seek Self-knowledge, which is Highest Bliss’.

•   The detailed teachings of Katha Upanishad have been variously interpreted, as Dvaita (dualistic) and as Advaita (non-dualistic).

•   It is one of the largest Upanishadic compilations.

•   The volumes are a motley collection of stories and themes.

•   As part of the poetic and chants focussed Samaveda, the broad unifying theme of the Upanishad is the importance of speech, language, song and chants to man's quest for knowledge and salvation, to metaphysical premises and questions, as well as to rituals.

•   It is presented as a dialogue between great sacrificer Saunaka and sage Angiras.

•   The Mundaka Upanishad is the source of the phrase Satyameva Jayate, which is the national motto of India. It appears in its national emblem with four lions.

•   The Kena Upanishad was probably composed sometime around the middle of the 1st millennium BC.

•   Kena Upanishad is notable in its discussion of Brahman with attributes and without attributes, and for being a treatise on "purely conceptual knowledge".

•   It is a foundational scripture to Vedanta school of Hinduism, for both the theistic and monistic sub-schools after varying interpretations.