Editing Upanishads (section)

===Principal Upanishads===
{{Main|Principal Upanishads}}
The Principal Upanishads, also known as the ''Mukhya Upanishads'', can be grouped into periods. Of the early periods are the ''Brihadaranyaka'' and the ''Chandogya'', the oldest.<ref>M. Fujii, On the formation and transmission of the JUB, [[Harvard Oriental Series]], Opera Minora 2, 1997</ref>{{refn|These are believed to pre-date [[Gautam Buddha]] ({{circa}} 500 BCE){{sfn|Olivelle|1998|pp=3–4}}|group=note}}

[[File:MS Indic 37, Isa upanisad. Wellcome L0027330.jpg|thumb|A page of ''[[Isha Upanishad]]'' manuscript]]
The Aitareya, Kauṣītaki and Taittirīya Upanishads may date to as early as the mid-1st millennium BCE, while the remnant date from between roughly the 4th to 1st centuries BCE, roughly contemporary with the earliest portions of the [[Sanskrit epics]]. One chronology assumes that the ''Aitareya, Taittiriya, Kausitaki, Mundaka, Prasna'', and ''Katha Upanishads'' has Buddha's influence, and is consequently placed after the 5th century BCE, while another proposal questions this assumption and dates it independent of Buddha's date of birth. The ''Kena'', ''Mandukya,'' and ''Isa Upanishads'' are typically placed after these Principal Upanishads, but other scholars date these differently.{{Sfn|King|1995|p=52}} Not much is known about the authors except for those, like Yajnavalkayva and Uddalaka, mentioned in the texts.{{sfn|Mahadevan|1956|p=56}} A few women discussants, such as Gargi and Maitreyi, the wife of Yajnavalkayva,{{sfn|Ranade|1926|p=61}} also feature occasionally.

Each of the principal ''Upanishads'' can be associated with one of the schools of exegesis of the four Vedas (''[[shakha]]s'').{{sfn|Joshi|1994|pp=90–92}} Many Shakhas are said to have existed, of which only a few remain. The new ''Upanishads'' often have little relation to the Vedic corpus and have not been cited or commented upon by any great Vedanta philosopher: their language differs from that of the classic ''Upanishads'', being less subtle and more formalized. As a result, they are not difficult to comprehend for the modern reader.{{sfn|Heehs|2002|p=85}}

{| class="wikitable"
|+ Veda-Shakha-Upanishad association
|-
! Veda!!Recension!![[Shakha]]!! Principal Upanishad
|-
| [[Rigveda|Rig Veda]]||Only one recension||[[Shakala]] || [[Aitareya Upanishad|{{IAST|Aitareya}}]]
|-
| rowspan=3|[[Samaveda|Sama Veda]]|| rowspan="3" |Only one recension ||Kauthuma || [[Chandogya|{{IAST|Chāndogya}}]]
|-
| [[Jaiminiya]]|| ''[[Kena Upanishad|Kena]]''
|-
|Ranayaniya ||
|-
|rowspan=7|[[Yajurveda|Yajur Veda]]|| rowspan="5" |Krishna Yajur Veda||Katha ||[[Katha Upanishad|{{IAST|Kaṭha}}]]
|-
|[[Taittiriya]]||[[Taittiriya Upanishad|{{IAST|Taittirīya}}]]
|-
|Maitrayani ||
|-
|Hiranyakeshi (Kapishthala)||
|-
|Kathaka ||
|-
|rowspan=2|Shukla Yajur Veda||Vajasaneyi Madhyandina||[[Isha Upanishad|{{IAST|Isha}}]] and {{IAST|[[Bṛhadāraṇyaka]]}}
|-
|[[Kanva Shakha]] ||
|-
|rowspan=2|[[Atharvaveda|Atharva Veda]]|| rowspan="2" |Two recensions|| [[Shaunaka]]||[[Mandukya Upanishad|{{IAST|Māṇḍūkya}}]] and [[Mundaka Upanishad|{{IAST|Muṇḍaka}}]]
|-
||Paippalada|| ''[[Prashna Upanishad]]''
|}