Scriptures of Sanatana Dharma - Upanishad

Original Text
IV. UPANISHADS
The Upanishads are the essence of Vedic teaching. They are called Vedantas meaning the concluding portion of the Vedas as well as the ultimate conclusions of Vedic wisdom. Upanishads happen to be the most foremost authorities of the Vedanta system of philosophy that developed in later times in different forms.
They reveal the most subtle and deep spiritual truths and are meant for Sanyasins. The collection of teachings generated by the ascetics who meditated on the mysteries of human existence came to be known as the Upanishads, which literally means "sitting close to" the teacher thereby indicating that the knowledge that it imparts is esoteric. Many, many Upanishads existed ages ago; a lot of them have been lost in the dark backward abysm of time. Only one hundred and eight have been preserved so far some in prose, some in verse. They are:
Upanishads of Rig-Veda
There are ten Rig-vedic Upanishads. They are
1 Ithareya Upanishad
2 Kausheethaki Upanishad
3 Nadhabindhu Upanishad
4 Aathmabhodha Upanishad
5 Nirvana Upanishad
6 Mulgala Upanishad
7 Akshamalika Upanishad
8 Tripura Upanishad
9 Sowbhagyalakshmi Upanishad
10 Bhahvrucha Upanishad
Upanishads of Sukla Yajur-veda
There are eighteen Sukla Yajur-vedic Upanishads. They are
1 Isovaasya Upanishad
2 Bruhadharanyaka Upanishad
3 Hamsa Upanishad
4 Paramahamsa Upanishad
5 Subhala Upanishad
6 Mantrika Upanishad
7 Thrisikibrahmana Upanishad
8 Niralamba Upanishad
9 Mandalabrahmana Upanishad
10 Adhwya Upanishad
11 Taraka Upanishad
12 Bhikshuka Upanishad
13 Adhyaatma Upanishad
14 Muktika Upanishad
15 Tarashara Upanishad
16 Yanjavalkya Upanishad
17 Shatyayana Upanishad
18 Turiyatheeya Avadhootha Upanishad
Upanishads of Krishna Yajur-veda
There are thirty two Krishna Yajur-vedic Upanishads. They are
1 Kada Upanishad
2 Thaiththireeya Upanishad
3 Brahma Upanishad
4 Kaivalya Upanishad
5 Swetaswetara Upanishad
6 Garbha Upanishad
7 Mahanarayana Upanishad
8 Amrithabindhu Upanishad
9 Amrithanadha Upanishad
10 Kalagnirudra Upanishad
11 Kshurika Upanishad
12 Sarvasara Upanishad
13 Shukarahasya Upanishad
14 Tejabindhu Upanishad
15 Dhyanabindhu Upanishad
16 Brahmavidhya Upanishad
17 Yogatatva Upanishad
18 Dhakshinamoorthy Upanishad
19 Skanda Upanishad
20 Saareerika Upanishad
21 Yogashika Upanishad
22 Ekakshara Upanishad
23 Akshi Upanishad
24 Avadhootha Upanishad
25 Kadarudra Upanishad
26 Rudrahrudhaya Upanishad
27 Panchabrahma Upanishad
28 Pranagnihotra Upanishad
29 Varaha Upanishad
30 Yogakundalini Upanishad
31 Kalisantarana Upanishad
32 Saraswatheerahasya Upanishad
Upanishads of Sama-veda
There are sixteen Sama-vedic Upanishads. They are
1 Kena Upanishad
2 Chandokya Upanishad
3 Aaruni Upanishad
4 Maitrayanee Upanishad
5 Maitreyee Upanishad
6 Vajrasuchika Upanishad
7 Yogachoodamani Upanishad
8 Vasudeva Upanishad
9 Maha Upanishad
10 Sanyasa Upanishad
11 Avyakta Upanishad
12 Kundika Upanishad
13 Savitri Upanishad
14 Jabhala Upanishad
15 Darsana Upanishad
16 Rudraksha Jabhala Upanishad
Upanishads of Atharva-veda
There are thirty two Atharva-vedic Upanishads.They are
1 Prasna Upanishad
2. Mundaka Upanishad
3. Maandukya Upanishad
4. Atharvasira Upanishad
5. Atharvasikha Upanishad
6. Bruhat Jaabhala Upanishad
7. Sita Upanishad
8. Sarabha Upanishad
9. Mahanarayana Upanishad
10. Ramarahasya Upanishad
11. Ramatapini Upanishad
12. Sandilya Upanishad
13. Paramahamsa Upanishad
14. Annapoorna Upanishad
15. Surya Upanishad
16. Aathma Upanishad
17. Pasuptha Upanishad
18. Parabrahma Upanishad
19. Tripuratapini Upanishad
20. Devi Upanishad
21. Bhavana Upanishad
22. Bhasma Jaabhala Upanishad
23. Ganapati Upanishad
24. Mahakavya Upanishad
25. Gopalatapini Upanishad
26. Sreekrishna Upanishad
27. Hayagriva Upanishad
28. Dhaththathreya Upanishad
29. Garuda Upanishad
30. Narasimhapurvatapini Upanishad
31. Naradapariprajaka Upanishad
32. Narasimha Uththaratapini Upanishad

Besides this 108 Upanishads, so many Upa-Upanishads are also there.