The Isha Upanishad (also known as Ishavasya Upanishad) is one of the shortest yet most profound and significant of the Principal Upanishads. It is unique in that it is embedded as the final chapter (40th Adhyaya) of the Shukla Yajurveda Samhita, making it the only Upanishad directly part of the Samhita portion of a Veda, rather than the later Brahmana or Aranyaka sections.