The Katha Upanishad (Devanagari: कठ उपनिषद्) (Kaṭhopaniṣad, also Kāṭhaka), also titled "Death as Teacher", is one of the mukhya ("primary") Upanishads commented upon by Shankara. It is associated with the Cāraka-Kaṭha school of the Black Yajurveda, and is grouped with the Sutra period of Vedic Sanskrit. It is a middle Upanishad. It contains passages that suggest contact with Buddhist ideas, so was likely composed after the fifth century BCE. It figures as number 3 in the Muktika canon of 108 Upanishads. It consists of two chapters (adhyāyas), each divided into three sections (vallis) that contain between 15 and 29 verses (ślokas) apiece. The Katha has some passages in common with the Gita. According to modern scholars, it propounds a dualistic philosophy.

Katha may be the most widely known amongst all the Upanishads; its early Persian translations first found their way into Europe. Max Müller translated it 1879, Edwin Arnold rendered it in verse, as "The Secret of Death" and Ralph Waldo Emerson gave the central story at the end of his essay, Immortality. Central to the text is the story of Nachiketa, son of sage Vajasravasa, and his encounter with Yama, Hindu God of death

Swami Atmajnanananda (also written Svāmī Ātmajñānānanda, born Stuart Elkman) is a swami (monk) of the Ramakrishna Order, which he joined in 1981. He has a Ph.D. in oriental studies from the University of Pennsylvania. He is currently resident minister at the Vedanta Center of Greater Washington, DC, in Silver Spring, Maryland, USA.

He authored Jiva Gosvamin's Tattvasandarbha: A Study on the Philosophical and Sectarian Development of the Gaudiya Vaisnava Movement, published by Motilal Banarsidass in 1986 under his pre-monastic name.

Atmajnanananda was a significant critic of Jeffrey Kripal's book Kali's Child.