Le Upanisad sono trattati, ora in versi, ora in prosa, di varia estensione e varia epoca. Essi rappresentano uno dei grandi sforzi compiuti dal genere
umano, per tentare di lumeggiare le verità supreme, offrendo una risposta alle domande fondamentali dell'uomo.
Le Upanisad di maggiore importanza sono quelle cosiddette "antiche" o "medie", oppure "vediche".
A queste opere, redatte grosso modo nell'arco di tempo che va dal 700 al 300 a.C., ne sono seguite molte altre, fino a tempi recenti.
Le Upanisad più antiche presentano una prosa assai vicina a quella dei Brahmana che le contengono.
Di nessuna di queste opere abbiamo il nome dell'autore.
Il monismo di stampo idealista che a più riprese permea di sè le maggiori tra le Upanisad, contrasta con il netto politeismo vedico.
La dottrina dell'Atman-Brahman e quella della trasmigrazione delle anime, paiono speculazioni riconducibili più ad ambienti della casta dei guerrieri che a quella, più formalmente ritualista,
di matrice brahminica. Ma queste sono solo supposizioni.
Le Upanisad vediche, infatti, vengono chiamate dalla tradizione indiana "Vedanta", ossia "la conclusione" dei Veda", quindi continuazione
e sviluppo ultimo dell'intero pensiero vedico.
La straordinaria fortuna delle Upanisad vediche è testimoniata dai numerosi, e importantissimi, commentari, che si sono succeduti nel corso dei secoli:
Gaudapada, Shankara, Madhva, Ramanuja e via dicendo, fino a Tagore e Aurobindo.
1. Isha Upanishad (detta anche Ishopanishad)
2. Kena Upanishad, o Kenopanishad
3. Katha Upanishad, o Kathopanishad
4. Prashna Upanishad, o Prashnopanishad
5. Mundaka Upanishad, o Mundakopanishad
6. Mandukya Upanishad, o Mandukyopanishad
7. Taittiriya Upanishad, o Taittiriyopanishad
8. Aitareya Upanishad, o Aitareyopanishad
9. Chhandogya Upanishad, o Chhandogyopanishad
10. Brihad-aranyaka Upanishad, o Brihad-aranyakopanishad
11. Brahma Upanishad, o Brahmopanishad
12. Kaivalya Upanishad, Kaivalyopanishad
13. Jabala Upanishad, Jabalopanishad
14. Shvetashvatara Upanishad, Shvetashvataropanishad
15. Hamsa Upanishad, Hamsopanishad
16. Aruneya Upanishad, o Aruneyopanishad
17. Garbha Upanishad, Garbhopanishad
18. Narayana Upanishad, o Narayanopanishad
19. Parama-hamsa Upanishad, o Parama-hamsopanishad
20. Amrita-bindu Upanishad, Amrita-bindupanishad
21. Nada-bindu Upanishad, o Nada-bindupanishad
22. Shira Upanishad
23. Atharva-shikha Upanishad (o Atharvashira Upanishad)
24. Maitrayani Upanishad
25. Kashitaki Upanishad
26. Brihaj-jabala Upanishad, o Brihaj-jabalopanishad
27. Nrishimha-tapaniya Upanishad, o Nrishimha-tapaniyopanishad
28. Kalagni-rudra Upanishad, o Kalagni-rudropanishad
29. Maitreyy-upanishad
30. Subala Upanishad, Subalopanishad
31. Kshurika Upanishad, o Kshurikopanishad
32. Mantrika Upanishad, o Mantrikopanishad
33. Sarva-sara Upanishad, o Sarva-saropanishad
34. Niralamba Upanishad, o Niralambopanishad
35. Shuka-rahasya Upanishad, o Shuka-rahasyopanishad
36. Vajra-sucika Upanishad, o Vajra-sucikopanishad
37. Tejo-bindu Upanishad, o Tejo-bindupanishad
38. Nada-bindupanishad, o Nada-bindupanishad
39. Dhyana-bindu Upanishad, o Dhyana-bindupanishad
40. Brahma-vidya Upanishad, o Brahma-vidyopanishad
41. Yoga-tattva Upanishad, o Yoga-tattvopanishad
42. Atma-bodha Upanishad, o Atma-bodhopanishad
43. Narada-parivrajaka Upanishad, o Narada-parivrajakopanishad
44. Trishikhi Upanishad
45. Sita Upanishad, o Sitopanishad
46. Yoga-cudamani Upanishad
47. Nirvana Upanishad, o Nirvanopanishad
48. Mandala-brahmana Upanishad, o Mandala-brahmanopanishad
49. Dakshina-murti Upanishad
50. Sharaba Upanishad, o Sharabopanishad
51. Skanda Upanishad, o Skandopanishad
52. Mahanarayana Upanishad, o Mahanarayanopanishad
53. Advaya-taraka Upanishad, o Advaya-tarakopanishad
54. Rama-rahasya Upanishad, o Rama-rahasyopanishad
55. Rama-tapani Upanishad
56. Vasudeva Upanishad, o Vasudevopanishad
57. Mudgala Upanishad, o Mudgalopanishad
58. Shandilya Upanishad, Shandilyopanishad
59. Paingala Upanishad, o Paingalopanishad
60. Bhikshu Upanishad, o Bhikshupanishad
61. Mahat Upanishad, o Mahadupanishad
62. Shariraka Upanishad, o Sharirakopanishad
63. Yoga-shikha Upanishad, o Yoga-shikhopanishad
64. Turiyatita Upanishad, o Turiyatitopanishad
65. Sannyasa Upanishad, o Sannyasopanishad
66. Paramahamsa-parivrajaka Upanishad
o Paramahamsa-parivrajakopanishad
67. Malika Upanishad, o Malikopanishad
68. Avyakta Upanishad, o Avyaktopanishad
69. Ekakshara Upanishad, o Ekaksharopanishad
70. Purna Upanishad, o Purnopanishad
71. Surya Upanishad, o Suryopanishad
72. Akshi Upanishad
73. Adhyatma Upanishad, o Adhyatmopanishad
74. Kundika Upanishad, o Kundikopanishad
75. Savitri Upanishad
76. Atma Upanishad, o Atmopanishad
77. Pashupata Upanishad, o Pashupatopanishad
78. Param-brahma Upanishad, o Param-brahmopanishad
79. Avadhuta Upanishad, o Avadhutopanishad
80. Tripuratapana Upanishad, o Tripuratapanopanishad
81. Devi Upanishad
82. Tripura Upanishad, o Tripuropanishad
83. Katha-rudra Upanishad, o Katha-rudropanishad
84. Bhavana Upanishad, o Bhavanopanishad
85. Hridaya Upanishad, Hridayopanishad
86. Yoga-kundalini Upanishad
87. Bhasma Upanishad, o Bhasmopanishad
88. Rudraksha Upanishad, o Rudrakshopanishad
89. Gana Upanishad, o Ganopanishad
90. Dharshana Upanishad, o Dharshanopanishad
91. Tarasara Upanishad, o Tarasaropanishad
92. Mahavakya Upanishad, o Mahavakyopanishad
93. Panca-brahma Upanishad, o Panca-brahmopanishad
94. Pranagni-hotra Upanishad, o Pranagni-hotropanishad
95. Gopala-tapana Upanishad, o Gopala-tapanopanishad
96. Krishna Upanishad, o Krishnopanishad
97. Yajna-valkya Upanishad, o Yajna-valkyopanishad,
98. Varaha Upanishad, o Varahopanishad
99. Satyayani Upanishad
100. Hayagriva Upanishad, o Hayagrivopanishad
101. Dattatreya Upanishad, o Dattatreyopanishad
102. Garuda Upanishad, o Garudopanishad
103. Kali Upanishad
104. Jabali Upanishad
105. Saubhagya Upanishad, o Saubhagyopanishad
106. Sarasvati-rahasya Upanishad, o Sarasvati-rahasyopanishad
107. Bahvrica Upanishad, o Bahvricopanishad
108. Muktika Upanishad, o Muktikopanishad.