Based on an extensive and successful hunt for previously unknown manuscripts containing the Jaiminīya-Upaniṣad-Brāhmaṇa, the late Professor Masato Fujii offers a critical edition of this text which provides many significant improvements to the two principal previous editions. This text is the earliest Upaniṣad (datable to c. 500 BCE), which in a unique way forms a transition from the Brāhmaṇas to the Upaniṣads. It is also an important text because of its Sāmavedic affinity, known for its arcane topics.The central theme is the “bodiless immortal gāyatra sāman”, developed by Śāṭyāyani, the original eponym of the Jaiminīya school of Sāmaveda.