The Isha Upanishad (Sanskrit: ईशोपनिषद्, IAST: Īśopaniṣad), also known as Shri Ishopanishad, Ishavasya Upanishad, or Vajasaneyi Samhita Upanishad, is one of the shortest Upanishads, embedded as the final chapter (adhyāya) of the Shukla Yajurveda. It is a Mukhya (primary, principal) Upanishad, and is known in two recensions, called Kanva (VSK) and Madhyandina (VSM). The Upanishad is a brief poem, consisting of 17 or 18 verses, depending on the recension.

It is a key scripture of the Vedanta sub-schools, and an influential Śruti to diverse schools of Hinduism. It is the 40th chapter of Yajurveda. The name of the text derives from its incipit, īśā vāsyam, "enveloped by the Lord", or "hidden in the Lord (Self)". The text discusses the Atman (Self) theory of Hinduism, and is referenced by both Dvaita (dualism) and Advaita (non-dualism) sub-schools of Vedanta.

It is classified as a "poetic Upanishad" along with Kena, Katha, Svetasvatara and Mundaka by Paul Deussen (1908).

Reference book:

1. Eight Upanisads Vol. 2 translated by Swami Gambhirananda - https://www.vedanta.com/store/Eight-U...