Names of Upanishad-1
See also    Alphabetical List of Upanishad

Upanishad are found in the concluding sections of Ved and are classified as Vedaant or the end of the Ved. There are five Ved with Yajur Ved having two versions. Each of these five books has several Shaakhaa (Branches). Each Shaakhaa has a Karm Khand dealing with the actions to be performed and is made up of Mantra and Braahman. The later deals with Upaasanaa or meditation and has Aaranyak inside them for the benefit of those who have resorted to the quiet habitat of the forest to pursue their spiritual Quest. The Upanishad are found mostly in the Aranyak section of the Ved. The five Ved have 1180 Shaakhaa and thus there should be 1180 Upanishad. But what we have now with us is a collection of 108 Upanishad. The list of these 108 Upanishad is given in the Muktikopanishad.

“The breakdown of the 108 Upanishads according to the five Ved are as follows:
1. Rig Ved: 10
2. Saam Ved: 16
3. Atharv Ved: 31
4. Krishn Yajur Ved: 32
5. Shukla Yajur Ved: 19

Major Upanishad
The ten major Upanishads which contain great philosophical discussions and knowledge are:

1. Eashaavaasya Upanishad
It is one of the great but brief Upanishad. It gives the summary of Indian philosophy very succinctly. It reviews the whole life and comes out with explanations.

2. Ken Upanishad
Kenopanishad derives its name from the first word Ken, meaning ‘by whom’. It belongs to the Talavakar Braahman of Saam Ved and is therefore also referred to as Talavakar Upanishad. It comprises 4 chapters and 35 Mantra. The first two chapters in verse and the other two chapters in prose. The metrical portion deals with the Supreme Unqualitative Brahm, the absolute principle underlying the world of phenomenon, and the prose part deals with the Supreme as God, 'Eeshwar'. 

In short it says that “The One Power that illumines everything and every one is indivisible. It is the Ear behind the ears, Mind behind the mind, Speech behind speech, Vital Life behind life. The ears cannot hear it; it is what makes the ears hear. The eyes cannot see it; it is what makes the eyes see. You cannot speak about it; it is what makes you speak. The mind cannot imagine it; it is what makes the mind think. It is different from what all we know; yet it is not known either. Those who feel they know Him, know Him not. Those who know that anything amenable to the senses is not Brahman, they know it best. When it is known as the innermost witness of all cognitions, whether sensation, perception or thought, then it is known. One who knows thus reaches immortality”.

The Kena Upanishad concludes that austerity, restraint, and work are the foundation of the mystical doctrine; the Ved are its limbs, and truth is its home. The one who knows it, strikes off evil and becomes established in the most excellent, infinite, heavenly world. The eternal question is, " At whose desire does the mind function, who puts first the vital force into motion?" The Rishi (seer of this Upanishad) answers, "The Brahm or the Transcendent and Immanent Spirit". It is neither seen by the eye nor heard by the ear. Nor the mind knows it. The Spirit is the seer of the eye, the hearer of the ear and knower of the mind. It is through the power of this Spirit that every thing else functions.

It is beyond the reach of the senses and can be felt like a mighty presence through intuition. It is that spirit which is real God and not the many gods that people worship. This is the teaching of ken Upanishad and is embodied in the allegory of Umaa, (also called Hemaavatee) the goddess of spiritual wisdom.

This Upanishad which is in the form of a dialog between Chaturmukh Brahmaa and Sadaashiv, and brings out the Sarv Prerakatwa (controller of all others), Sarvottamatwa (superiority over all else) and Sakalyena Avedyatwa (Unknowable in its entirety) of the Supreme Person. The Upanishad asks three questions at the outset:
(1) Who directs the mind towards its good or bad objects?
(2) Who directs Mukhya Praan to discharge his duties?
(3) Who directs the senses - eye, ear, etc, towards the respective objects?

All these questions have but a single answer. He who gives the power of seeing to the eye, hearing to the ear, thinking to the mind and power to move to Praan directs their respective activities. He is evidently the Supreme God. Those who realize that He is the director of the mind, senses and even of Praan, will attain liberation. This takes us to the question of the nature of God.

God is beyond the reach of the senses, beyond words and even beyond the mind. Being Infinite, He cannot be brought within the compass of limited knowledge. One cannot know how He directs the senses, mind, etc. However, He does not remain altogether unknown, but is not completely known because of His infinite nature. He is unique, distinct from and Superior to all known things manifest or un-manifest. He cannot be known through speech, mind, eyes, etc, but knows all that is known through these and regulates them. He is immanent in all the Jeev and directs them, but He is not identical to them. Those who think that they know Him fully do not really know Him, as they have not comprehended His Infinite nature. On the other hand, those who think that they do not know Him fully, know Him, as they have realized His Infinite nature. The knowledge of God to the best of one's ability is adequate for one's salvation. The presence of God as the Inner resident and controller of all is brought out by an interesting story of Ahankaar Khandan (humbling the pride) of Agni, Nasikya Vayu and Indra in this Upanishad.

The Upanishad concludes its teaching by stating that Tapas (penance), Dam (subduing the senses) and Karm (prescribed action) are the means to obtain spiritual knowledge. The Ved, Vedangas and Meemansaa constitute the source literature of philosophical inquiry.

3. Kathopanishad
“The Kath Upanishad is divided into six Vallee. Vallee literally means a creeper. A Vallee, like a creeper, is attached to the Shaakhaa or Branches of the Ved. This Upanishad is also divided into two Adhyaaya (chapters) of three Vallee each. “This is one of the most beautiful Upanishad in which the eternal truths are given in the form of a narrative. The narrative is taken from Taittireeya Braahman (3-11-8) with some variation. The same story is told in the Taittireeya Braahman, only with this difference that in the Braahman, freedom from death and birth is obtained by a peculiar performance of a sacrifice, while in the Upanishad it is obtained by knowledge only.”

4. Aitareya Upanishad
The Aitareya Upanishad is one of the oldest of the Upanishads. It belongs to the Aitareya Aaranyak of the Rig Ved. It is divided into three chapters and contains only 33 verses. The Upanishad deals with the process of creation.

5. Brihadaaranyak Upanishad
“Brihadaaranyak Upanishad means the "great forest-book". This Upanishad is one of the oldest of all the Upanishad. It consists of three sections or Kaand: the Madhu Kaand, the Yaagyavalkya or the Muni Kaand and the Khilaa Kaand. Here the Braahman is portrayed as universal and undifferentiated consciousness. The doctrine of the indescribability of the absolute and the doctrine of 'Neti, Neti' are explained. This Upanishad concludes by stating the three virtues that one should practice ie self-restraint, giving, and compassion.”

6. Prashn Upanishad
“In Sanskrit, Prashn means question. This book consists of six questions and their answers, hence the name. It is in the form of question-answers. Except first and last questions, all other questions are actually a group of smaller sub-questions. As narrated in the beginning of this Upanishad, Six pupils interested in knowing divinity or Braahman come to the sage Pippalaad and ask questions of great spiritual importance. Pippalaad asks them to take up penance of one year. Upon completion of penance, they again come to the sage and ask questions, then the sage answers their questions.”

7. Maandookya Upanishad
“For the very reason that it explains the esoteric meaning of the fundamental syllable Aum of Hindu spiritual tradition, the Upanishad has been extolled greatly. The Muktikopanishad which talks about all other Upanishads, says that if a person cannot afford to study all the hundred and more Upanishads, it will be enough to read just the Maandookya Upanishad. According to Dr S Radhakrishnan in this Upanishad we find the fundamental approach to the attainment of reality by the road of introversion and ascent from the sensible and changing, through the mind which dreams, through the soul which thinks, to the divine within but above the soul.”

8. Taittireeya Upanishad
“The Taittireeya Upanishad belongs to the Taittireeya school of the Yajur Ved. It is divided into three sections called Vallee. The first is the Shikshaa Vallee. Shikshaa is the first of the six Vedaang (limbs or auxiliaries of the Ved); it is the science of phonetics and pronunciation. The second is the Brahmaanand Valle and the third is the Bhrigu Vallee. These two deal with the knowledge of the Supreme Self, Paramaatmaa Gyaan.”

9. Chhandogya Upanishad
“Along with Brihadaaranyak Upanishad the Chhaandogya Upanishad is an ancient source of principal fundamentals for Vedaant philosophy. Considering number of references made to this Upanishad in Brahm Sootra, it indicates special importance of this Upanishad in Vedaant philosophy. Important spiritual practices like Dahar Vidyaa, Shaandilya Vidyaa, etc are its specialty.”

It comprises eight chapters with several sections in each, all in prose.
The 1st and the 2nd chapters concentrate on meditation and begin with Upaasanaa on OM, the best symbol of Paramaatmaa. Shankar considers that some deities assumed the form of dogs and revealed the Udgeet to sage Bagadaalbhya.
Its 3rd chapter deals with the meditation on Aaditya (Sun) and is also called Madhu Vidyaa. It also gives the famous Shaandilya Vidyaa which prescribes meditation on Atman which is identified with Brahman(tajjallan) .
The 4th chapter provides four vidyas- Samvargavidya, ShOdasha kalaavidya, UpakOsalavidya and Akshipurushavidya.
The 5th chapter shows three kinds of destination for the soul - (1) Those who practice Panchaagni Vidyaa (meditation on the five fires) will go by Archiraadi Maarg (path of light) to Brahm Lok and will not return. (2) Those performing rituals without enlightenment will go by Dhoomaadi Maarg (Path of smoke) and attain Pitri Lok from which they return to human world. (3) Those leading a beastly life without any of these will constantly go through the life of births and deaths.

The last three chapters contain the essence of Vedaant philosophy.
The 6th chapter deals with the knowledge of meditation on Sat (Brahm) and is in the form of a dialog between Uddaalak Aaruni and his son Shwetaketu. The son had returned after a 12 year study and had some arrogance about his knowledge. The father questions as to whether he knows that by knowing which every thing will be known. The boy then requests his father to teach it to him. Taking the examples of clay, gold and iron and their products like pot, ornaments etc, the father draws attention towards the identity between the cause and its effects. He asserts that the names and forms are unreal and the substance alone is real.

Applying the same principle, he says that before creation, Sat alone existed and it evolved into this world of names and forms through the three primary elements-fire, water and earth (Tej, Aap and Anna). The individual self- the Jeev, merges into Sat during the state of deep sleep. Since ignorance still persists, he comes back to the original state. The same logic applies for rebirth after death also. Those who attain knowledge get liberated from this cycle. The famous Vedaantik dictum, the Mahaa Vaakya, "Tat Twam Asi" appears for the first time in the 8th section and is repeated later 9 times. The purport of the whole of the sixth chapter is to teach the identity of the Jeevaatmaa or the individual self with Brahm or the cosmic soul. This chapter is thus the most instructive and interesting part of the Upanishad.

Though Naarad had mastered several things, he had no peace of mind and Sanat Kumaar takes him step by step through several modes of Upaasanaa to Bhooman or Brahman.
The 8th chapter realizing that it is difficult to comprehend and contemplate on the Nir-Gun Brahm, advises meditation on the quality aspect of Brahm (Sa-Gun Brahm). It starts with Daharaa Vidyaa (meditation on the self within the small Aakaash of the heart. Here also, Prajaapati teaches Indra about Aatmaa, the true self within.
Chhaandogya Upanishad is thus a unique text giving an insight into the philosophical inquiry of the highest kind.
Shankar has written a voluminous commentary on it.

10. Mundak Upanishad
“This Upanishad begins with an Invocation, praying that eye may see auspicious things, the ear may hear auspicious sounds, and that life may be spent in the contemplation of the Lord. The teaching of this Upanishad is referred to as Brahm Vidyaa, either because it describes first the message of Hiranyagarbh, the casual Brahm, or because the message relates the glory of Braahman. This Upanishad speaks of Brahm Vidyaa as the mystery which only those with shaven heads and those who go through a rite of having Fire on the shaven head can understand. So, it is called Mundak, or shaven Head. Apart from this, this Upanishad is honored as the crest of all, since it expounds the very essence of Brahm Gyaan. It is assigned to the Fourth Ved - the Atharv Ved.”
(The write up about the ten major Upanishads has been taken from various web sites. My indebtedness to those great souls who have written them is greatly acknowledged.)