(1) General (of common interest), (2) Shaiv (Dealing with Lord Shiv), (3) Shaakt (dealing with the Divine mother Shakti), Vaishnav (dealing with Lord Vishnu), Sanyaas (dealing with renunciation) and Yog (dealing with Yaugik practices) Upanishad. Though classification is made, still there is some overlapping in the subjects dealt with. Short notes on each of these Upanishad category wise are given below:

(2) Garbh Upanishad
This Upanishad is by sage Pippalaad and deals with the growth of fetus in the womb. It also gives the number of different parts of the body like bones, nerves, flesh etc.

(3) Maitraayaneeya or Maitree Upanishad
This Upanishad tells us about the penance of a king called Brahadrath. The King asks the sage Shakanya about the feeling of desire in this meaningless world. Sage Shakanya relates him, what has been told to him by sage Maitreya. He teaches him the great science of Brahm Vidyaa. And tells him finally that mind and illusion are responsible for this contradiction.

(4) Kaushitakee Upanishad
This Upanishad is taught by sage Chitra to sage Uddaalak and his son Shwetketu. It deals about the science of soul. The temporary nature of rituals and good deeds and permanent nature of doing everything without desire is emphasized. It also tells the need for a father to give up all his personality and knowledge to his son and enter Sanyaas.

(5) Subal Upanishad
This is the teaching of Sage Angiraa to sage Raikwa. It tries to answer the question of the time and method of creation of the world. It also tries to find out the properties of the soul of beings and has several aspects of philosophy.

(6) Maantrik Upanishad
Deals about the properties of Braahman. Tells that whatever is produced vanishes and then is reproduced. Concludes that the one who knows it well is the Braahman.

(7) Sarvaasar Upanishad
Defines and explains several words like Kath, Bandh, Annamaya etc, which occur constantly in Upanishadik philosophy.

(8) Nirlamb Upanishad
It is an independent text of Hindu philosophy. It tries to investigate what is Brahm and concludes that the Sanyaasee by following proper methods has a better chance of attaining salvation.

(9) Shuk Rahasya Upanishad
This Upanishad is supposed to be taught to sage Shuk so that he would understand the philosophy of salvation. The explanations of words and ideas are extensive.

(10) Vajrashoochikaa Upanishad
This Upanishad investigates and tries to answer the question, “Who is a Braahman? It says that caste does not come by birth.

(11) Aatm Prabodh Upanishad
Tells us about meditation on Pranav and the great Vaishnav Mantra ”Om Naaraayanaaya Namah”. Defines and tells about the identities of an evolved soul.

(12) Skand Upanishad
Takes a conciliatory stand between Shaiv and Vaishnav. Tells that both are same.

(13) Mudgal Upanishad
This Upanishad aims at explaining the Mantra of the great Purush Sookt.

(14) Paingal Upanishad
This is taught by sage Yagyaavalkya to sage Paingal. It gives an explanation of the term ‘Kaivalya’. It also attempts to explain the Mahaa Vaakya of Ved like ‘Aham Brahmasmi’ as well the duties of Gyaanee.

(15) Mahat Upanishad
Tells about the initial creation of the universe starting From Lord Naaraayan till Lord Brahmaa. After this there is discussion between sage Shuk and the King Janak regarding the creation of the Sansaar. This is followed by discussion of several aspects of philosophy between Sage Nidaagh and his Guru Sage Ribhu. It tells that Shaastra are burden for a Gyaanee, Gyaan is a burden to those who are attached and so on.

(16) Shaareerik Upanishad
Tells us about the different aspects of the human body, including states of knowledge.

(17) Aksha-maalikaa Upanishad
This Upanishad is taught by Guha to Lord Brahma. It tells us in detail about how to choose the Maalaa (rosary) for use in meditation.

(18) Ekaakshar Upanishad
This is an Upanishad which deals with the letter "Aum". This is more of a prayer towards "Aum".

(19) Soorya Upanishad
Tells us about Soorya Angiraa Mantra and Gaayatree which is a prayer to the Sun. Tells also about the Ashtaakshar to worship Lord Surya.

(20) Akshi Upanishad
Contains the prayer of sage Sankriti to Lord Soorya which contains the Chaakshushmatee Mantra. This is followed by teaching of Brahm Vidyaa by Soorya.

(21) Adhyaatm Upanishad
This is initially taught by Sadaashiv to sage Apaantaraatam. Tells that there is nothing but Aatmaa and the feeling of existence of others is only illusion.

(22) Saavitree Upanishad
Tells us who is Saavitree and the difference between Savitaa and Saavitree. Also gives the Saavitre Mantra.

(23) Aatm Upanishad
Deals with various aspects of Aatmaa and how a Brahm Gyaanee does not see any other thing except Aatmaa.

(24) Kath Rudra Upanishad.
This is teaching of Brahma Vidyaa by Lord Brahma himself to the Devas. The treatment is philosophical.

(25) Panch-Brahm Upanishad
Details the five stages by which Par-Brahm was evolved.

(26) Praan Agnihotra Upanishad
This Upanishad deals with the Shareer Yagya or the sacrifice to the body. Tells what all Mantras are to be chanted before taking food. The usual Mantra that a Braahman chants while taking food are contained in this Upanishad.

(27) Muktik Upanishad
This Upanishad is the Teaching of Lord Raam to Hanumaan. It tells about Ved, Vedaang and also Kaivalya and also summarizes the Hindu Vedaant. The list of 108 Upanishad is given in this Upanishad.

(2) Atharv-shir Upanishad
It emphasizes about the greatness of the holy letter “Aum”. It also tells that the form of Lord Rudra is the form of Pranav.

(3) Atharv-shikhaa Upanishad
This is taught by Sage Adarv to great sages like Pippalaad, Angiraa and Sanat Kumaar. It emphasizes on the need and benefits on the meditation of the Pranav.

(4) Brihajjaabaal Upanishad
This Upanishad is told by Kaalaagni Rudra to sage Bhushundi. It deals in detail about the method of preparation of holy ash (Vibhooti) and method of wearing it.

(5) Kaalaagni Rudra Upanishad
It tells in detail about the method of wearing holy ash (Vibhooti) along with Mantra for wearing the same. This is taught by Kaalaagni Rudra to the great sage Sanat Kumaar.

(6) Dakshinaamoorti Upanishad
Dakshinaamoorty is the teacher form of Shiv. He teaches without talking. This Upanishad gives the Dakshinmoorti Mantra and the method of practicing it.

(7) Sharabh Upanishad
Sharabh is the animal, man and bird form of Lord Shiv. It is believed that he took this form to control the anger of Vishnu when he took the form of Narasinh. This Upanishad tells about Lord Sharabh.

(8) Pashupat Brahmopanishad
Tells us lord Shiv’s aspect of Pashupati (the Lord of all living things). Tells how that the entire universe is really one and there is no differentiation.

(9) Rudra Hridaya Upanishad
Shuk asks his father which God exists in all Devtaa and in which God all Devtaa exist. The answer is this Upanishad. He tells that it is Rudra.

(10) Bhasm Jaabaal Upanishad
Tells about how Vibhooti has to be prepared and also the daily duties of a Braahman. This is the teaching Lord Shiv to Jaabaal Bhushund.

(11) Rudraaksh Jaabaal Upanishad
This is the teaching of Kaalaagni Rudra to sage Bhushund and deals exclusively about Rudraaksh.

(12) Ganapati Upanishad
Starts with a prayer to Lord Ganapati and gives the Ganapati Mantra. Tells how to worship Ganapati.

(13) Jaabaali Upanishad
Sage Jaabaali tells sage Pippalaad about Lord Pashupati. The need and method of wearing Vibhooti (Holy ash) is given in detail.

(2) Tripur Taapinee Upanishad
Tells about the Shataaksharee Mantra for meditating on Tripur, the Goddess Paarvatee. Several great Mantra like Gaayatree, and Panchaadash Aksharee are a part of this. Tells about Shree Vidyaa Upaasanaa.

(3) Annapoornaa Upanishad
Sage Rupu tells sage Nidaagh about Devee Annapoornaa. He also teaches him the Annapoornaa Mantra. This is followed by teaching of philosophical aspects like Maayaa, Yog and Mukti.

(4) Devee or Devya Atharvaa Sheersh Upanishad
The Devee tells the Devtaa in this Upanishad who she is, about Panchdash Aksharee and Nava Aksharee Mantra to worship her.

(5) Tripur Upanishad
Tells about Shree Chakra and the worship of the Devee through the right and left methods.

(6) Bhaavanaa Upanishad
Tells one important aspect of Shree Vidyaa Upaasanaa.

(7) Saubhagya Lakshmee Upanishad
Bhagavaan Naaraayan tells about the Shakti from whom every God originated and teaches the Dev, the worship of Saubhaagya Lakshmee.

(8) Saraswatee Rahasya Upanishad
This Upanishad is taught by Sage Asvalayan to other sages. He teaches them the ten Saraswatee Mantra and methods of worshipping her.

(9) Bahuvrachaa Upanishad
Talks in detail about the existence of Shakti from whom all gods and knowledge originated. Gives hints of worship of Shree Vidyaa.

(2) Narasinh Taapinee Upanishad
It has two parts. In the Poorv part, it tells in detail about the greatness of Lord Naraimha. It also has the great king of Mantras called Narasinh Mantra and tells in detail how to meditate on it. In the Uttar part it tells also about the greatness of Pranav and the Narasinh Raja Mantra. It gives detailed method of meditating on Lord Narasinh.

(3) Tripad Vibhooti Mahaa-naaraayan Upanishad
Brahmaa did Tap for 1000 years to know from Lord Vishnu about Brahm. This is what Lord Vishnu told him. Also clears his doubts such as Braahman having a form and not having a form etc. Also gives the shapes of several Yantra.

(4) Raam Rahasya Upanishad
Tells that Lord Raam is Brahm Taarak and expounds various Mantras for worshipping him. Also gives Yantra for worshipping Lord Raam.

(5) Raam Taapinee Upanishad
There are two parts, the Poorv Taapinee and the second Uttar Taapinee. Tells about the greatness of the word “Raam”. Tells about the Raam Yantra, which is similar to the Shree Chakra. Tells also the belief that ‘Lord Shiv tells the Taarak Mantra in the ears of all people dying in Varanasi’ and the method of worship of Raam.

(6) Vaasudev Upanishad
Tells about what is Oordhwa Pundra (the sign worn by Vaishnavites) and the rules for wearing it.

(7) Avyakt Upanishad
Deals about the creation of clearly defined things from that unclear past. Tells how Prajaapati came from Avayakt and went on to create the world. Gives a Mantra to worship Lord Vishnu.

(8) Taaraasar Upanishad
Tells about holiness of Kurukshetra, Taarak Mantra and Pranav. Tells method of worship of Lord Naaraayan.

(9) Gopaal Taapinee Upanishad
Sages approach Lord Brahmaa to know the procedure to worship Krishn. What he tells them is contained in this Upanishad. The Upaasanaa Mantra of Govind is given.

(10) Krishn Upanishad
The sages when they meet Raam, they wanted to embrace Him. He made them to be born as Gopee and He took the Avataar of Krishn, so that they can embrace him. This book tells as to who were born as what in Krishnaavataar.

(11) Hayagreev Upanishad
Brahmaa Jee tells Naarad that whoever meditates and worships Lord Hayagreev gets to know the Brahma =Vidyaa. The Mantra for worship of Lord Hayagreev is also given.

(12) Dattaatreya Upanishad
Tells the method of meditation and worship of Dattaatreya. The Dattaatreya Mantra is given.

(12) Garud Upanishad
The method of meditation and worship of Garud, the vehicle of Lord Vishnu is given.

(13) Kali Santaaran Upanishad
Tells about how the evils of Kali age is to be crossed. The 16-letter prayer on Raam would help one in doing this.

(2) Jaabaal Upanishad
This is compiled by Sage Jaabaal. This gives more emphasis on meditation and the chanting of Rudra. The greatness of concentrating between the centers of eyes is stressed here.

(3) Aarunya Upanishad
This Upanishad deals about the teaching of Prajaapati to sage Aaruni. It gives in detail the rules of life to be followed by a Brahmchaaree and a Sanyaasee.

(4) Paramhans Upanishad
It deals about the discussion between Sage Naarad and God on who is a Paramhans (Sanyaasee at an advanced stage) and methods to identify him.

(5) Maitreyee Upanishad
It is the teaching of Lord Parameshwar to sage Maitrey. To a large extent, what is given in Maitrayani Upanishad is repeated here. In addition God tells to him in detail about his formless form.

(6) Nirvaan Upanishad
Details about the Sanyaas Maarg involving Nirvaan (nudity). Tells about how the people follow it.

(7) Naarad Parivraajak Upanishad
This is the teaching of Naarad to the Souunaka Sages. It tells about the methods to attain salvation, the rules to be followed by a Sanyaasee, and the time when a person should enter Sanyaas. It also talks about Karm Sanyaas.

(8) Bhikshuk Upanishad
It defines the different types of Sanyaasee like Kuttesak, Bahoodhak, Hans and Param Hans.

(9) Turiyateeya Upanishad
It is taught by Lord Naaraayan to Lord Brahmaa and tells us abut the rules of the life of an Avadhoot.

(10) Sanyaas Upanishad
Tells who can take Sanyaas and what is the procedure.

(11) Param Hans Parivraajak Upanishad
This is taught by Lord Naaraayan to Lord Brahmaa. It deals mainly about the procedure of taking Sanyaas.

(12) Kundik Upanishad
Tells what al things a Sanyaasee should possess. And how he should behave.

(13) Parabrahm Upanishad
Tells what is Yagyopaveet as well as Shikhaa, for the Sanyaasee as well as people of the world. Gives clearly the total length of the Upa-veet. For the Sanyaasee it is the Pranav which acts as Yagyopaveet and Shikhaa.

(14) Avadhoot Upanishad
Dattaatreya teaches sage Sankriti as to who is Avadhoot and how he should behave.

(15) Yaagyavalkya Upanishad
The Upanishad tells when to assume Sanyaas and also the properties of a Sanyaasee.

(16) Saatyaayanee Upanishad
Mind becomes the reason for attachment and salvation. Tells that a real Braahman should search for Brahm. Also tells that one taking Sanyaas gives redemption for three generation of manes.

(2) Hansopanishad
This talks about meditation on Hans Mantra and is being taught by sage Gautam to sage Sanat Kumaar. The method of meditating on the Has Mantra is fully described.

(3) Amrit Bindu Upanishad
It gives the knowledge of Aatmaa in the tasty form of nectar and gives it as briefly as a dot. It tells us about what is Brahm and other concepts of hard core Hindu Philosophy.

(4) Amrit Naad Upanishad
This describes the way and detailed method to chant the holy letter “AUM", which is called here as the nectar like letter.

(5) Ksharik Upanishad.
Ksharik means knife. It is so called because it cuts ignorance using the knife of wisdom. This is a Upanishad which in detail tells about Yog and its practice.

(6) Tejo Bindu Upanishad
This Upanishad is the teaching of Lord Param Shiv to his son Subramanya. Talks in detail about Yaugik practices, defines Chinmaya Swaroop, Aatmaanubhav, Jeevan Mukt etc.

(7) Naad Bindu Upanishad
Tells in detail about the meditation on Omkaar (Pranav). The method of meditation and some problems which may occur are pointed out.

(8) Dhyaan Bindu Upanishad
The meditation on Pranav and A-japaa Gayatree is dealt in detail along with the method involved.

(9) Brahm Vidyaa Upanishad
Teaches methods of attaining Brahm through meditation. Emphasizes role of Guru. Tells that Sruti is more important than Pramaan.

(10) Yog Tattwopanishad
This is the teaching of Lord Vishnu to Lord Brahmaa. It details out the Yaugik practice. It also tells about the stages in Yog, defines them and tells how to recognize them.

(11) Trishikee Braahmanopanishad
This is the teaching of Lord Soorya to a Braahman called Trishikee Braahman. He clears his doubts about the definition of the body, soul, Karan and Yaugik practice.

(12) Yog Choodaamani Upanishad
Tells about Yaugik practice involving A-japaa Gaayatree. Tells about the seats of Yog, tells how to wake up the Kundalinee and reach her up to Brahm Randhra.

(13) Mandal Braahmanopanishad
This is the teaching of Sun God to his disciple Yaagyavalkya. This deals with the principle of the soul through yogic practice. Definitions of various terms used in Yog is also given. Tells in detail about Yaugik practice and tells us about what is Sambhaavee Mudraa.

(14) Shaandilya Upanishad
This is taught by sage Atharvaa to sage Shaandilya. It deals with Ashtaang Yog and Brahm Vidyaa.

(15) Yog Shikhaa Upanishad
This is the teaching of Lord Maheshwar to Lord Brahma. It deals with subjects like Mukti, Shakti, Naad, Chaitanya and Yog.

(16) Yog Kundalinee Upanishad
Tells about Kundalinee and Yaugik practice.

(17) Shree Jaabaal Aadarsano Upanishad
This is the teaching of Lord Dattaatreya to his disciple sage Sankriti. And tells how the Yog should be done in detail.

(18) Mahaavaakya Upanishad
Confirms that the knowledge “That this Sun is Brahm” would be realized by chanting of A-japaa Gaayatree. Tells what is the merger of mind with Brahm.