The literature on Tantras is vast and variously classified. According to Mṛgendra Tantra, Parameśvara, to award the four puruṣārthas to souls, classified the primordial ocean of knowledge into Pancasrotas. These are well known as ūrdhva, pūrva, dakṣiṇa, uttara, and paścima. From the great Niṣkala known as Paramaśiva, this knowledge first emanates as nāda and corresponding to the bhūmi named Sadāśiva, it attains the form of Tantra. According to Kāmikāgama, the five divisions listed above emanated from the five faces of Sadāśiva. The same āgama classifies the ocean of knowledge into laukika, vaidika, ādhyātmika, atimārga, and mantrātmaka. As each of these emanated from the five faces, their total count is twenty-five. Sarvātmaśambhu, in his Siddhāntadīpikā, discusses the details of laukika and other classifications. The branch of mantrātmaka tantra is again of five types based on the vaktra of Sadāśiva from which it originates. That emanating from the ūrdhvavaktra is called Siddhāntāgama and is said to confer Mukti or liberation. Gāruḍa tantra emanates from the eastern face and is capable of destroying poisons of all kinds. The Vāma tantras emanating from the northern face of Sadāśiva are aimed at vaśīkaraṇa. The Bhūta tantra emanating from the western face aims at subjugating bhūtagraha. Bhairava tantra emanating from the southern face is aimed at śatrukṣaya.
The followers of āgama hold Siddhānta jnāna to be superior to Vedādi jnāna. Even there, there is a two-fold division: śivajnāna and rudrajnāna. Again, these two are classified into para and apara. The classification described so far is pertaining to śāstra that is śabdajnānātmaka. The knowledge from Niṣkala which is avabodharūpa is again of different types of jnāna: śuddha mārga, aśuddha mārga, of śiva, of paśu etc. The knowledge that is of the form of dīkṣā or initiation is also of several types: naiṣṭhika, bhautika, nirbīja, sabīja, śivadharmī, and lokadharmī. Hence, Svāyambhuva āgama states that though the primordial knowledge that emanates from Paramaśiva is one, it assumes various forms based on the receiver of this knowledge. Thus, śivajnāna is of 10 kinds and rudrajnāna of 18 kinds. Again, these vary based on the lineage of propagation. There are two paramparās in the case of śivāgama and two for Rudrāgama. Thus, a total of 30+36=66 āgamas is to be arrived at here.
The following list of ten śivāgamas is from Kiraṇāgama and also indicated here is the line of transmission of these āgamas:
1. Kāmika- praṇava, trikala, hara
2. Yogaja- sudhā, bhasmaga, prabhu
3. Chintya- dīptākhya, gopati, ambikā
4. Kāraṇa- kāraṇākhya, śarva, prajāpati
5. Ajita – suśiva, umeśa, acyuta
6. Sudīpta- īśa, trimūrti, hutāśana
7. Sūkṣma- sūkṣma, bhava, prabhanjana
8. Sahasra – kāla, bhīma, manas
9. Suprabheda – gaṇeśa, avighneśa, śaśi
10. Amśumān – amśu, agra, ravi
The following is a list of Rudrāgamas from the same āgama:
1. Vijaya – anādi, parameśvara
2. Parameśvara – śrīrūpa, uśanā
3. Niḥśvāsa – daśārṇa, śailasambhavā
4. Prodgīta – śūlī, kaca
5. Mukhabimba – praśānta, dadhīci
6. Siddhamata – bindu, caṇḍeśvara
7. Santāna – śivaniṣṭha, haṃsavāhana
8. Nārasiṃha – saumya, nṛsiṃha
9. Chandrahāsa – ananta, bṛhaspati
10. Bhadra – sarvātmā, vīrabhadra
11. Svāyaṃbhuva – nidhana, brahmā
12. Viraja – teja, prajāpati
13. Kauravya – bradhneśa, nandikeśvara
14. mākuṭa – śiva, dhvajāśraya
15. Kiraṇa – devapitā, saṃvartaka
16. Lalita – ālaya, bhairava
17. āgneya- vyoma, hutabhuk
18. ? – śiva, ?
In the Jayarathī ṭīkā on Tantrāloka, one sees a list quoted from śrīkaṇṭhī saṃhitā with some differences. In that list of ten śivāgamas, Kāraṇa is replaced by Makuṭa and Sudīpta by Dīpta. Kāraṇa is a pratiṣṭhā tantra rumored to have a hundred lakh ślokas and is said to have been propagated by Lord Rudra to Brahmā. It is composed of four saṃhitās.
According to śrīkaṇṭhī mata, the ten śivāgamas are bheda-pratipādaka or espousing a dualistic philosophy. Also, the eighteen Rudrāgamas are said to be of the bhedābheda category. If this list from Kiraṇāgama is compared with that in śrīkaṇṭhī saṃhitā, Prodgīta is replaced by Madgīta, Chandrahāsa by Chandrāṃśu, Bhadra by Vīrabhadra, Viraja by Visara, Kauravya by Raurava and Mākuṭa by Vimala. Some other works replace Mukhabiṃba by Chandrajnāna, Nārasiṃha by Visara, etc.
In Niḥśvāsatantra saṃhitā, the uttarasūtra section lists eighteen ancient śivasūtras: vijaya, niḥśvāsa, svāyaṃbhuva, vātula, vīrabhadra, raurava, mākuṭa, virasa, chandrahāsa, jnāna, mukhabimba, prodgīta, lalita, siddha, santāna, sarvodgīta, kiraṇa and pārameśvara.
Some works and authors seem to hold that most of these āgamas were popular more in the Northern part of India as Brāhmaṇas of āryāvarta are described as more suited for the role of a śivācārya in comparison with dvijas from Kāmarūpa, Kāśmīra, Kaliṅga, Koṅkaṇa, Kāncī, Kāverī, and other places.
Apart from these, the list of 64 tantras is quite popular in various tantric literature. śrīkaṇṭhī saṃhitā calls these Bhairavāgama and describes the philosophy therein to be Advaita or non-dual. Vāmakeśvara Tantra also produces such a list. Commentaries on this include ṛjuvimarśinī and Artharatnāvalī and both these examine the list of 64 tantras. Even the great Bhāskararāya examines the list in his Setubandha. Achārya Shaṅkara also speaks of the sixty-four tantras in his Saundaryalaharī. In his commentary on Saundaryalaharī, Lakṣmīdhara rejects the entire list of sixty-four tantras as avaidika. However, Bhāskararāya disagrees with him and argues against considering all of the tantras as avaidika. Sarvānanda, in his Sarvollāsa Tantra, lists sixty-four tantras, based on a list said to be from Toḍalottara Tantra.
The list of sixty-four tantras from śrīkaṇṭhī saṃhitā:
Group of Bhairava Tantras: svacchanda, bhairava, caṇḍa, krodha, unmattabhairava, asitāṅgabhairava, mahocchuṣma, kapālīśa.
Group of Yāmala tantras: brahmayāmala, viṣṇuyāmala, svacchandayāmala, ruruyāmala, atharvaṇayāmala, rudrayāmala, vetālayāmala.
Group of Mata-tantras: rakta, laṃpaṭa, raśmimata, mata, cālikā, piṅgalā, utphulla, viśvavandya.
Group of Mangala tantras: picubhairavī, tantrabhairavī, brāhmīkalā, vijayā, candrā, maṅgalā, sarvamaṅgalā.
Group of Chakrāṣṭaka tantras: mantracakra, varṇacakra, śakticakra, kalācakra, binducakra, nādacakra, guhyacakra, khacakra.
Group of Bahurūpa tantras: andhaka, rurubheda, aja, mūla, varṇa, naṣṭa, mātṛkā, jvālinī
Group of Vāgīśa tantras: bhairavī, citrikā, haṃsa, kadambikā, hṛllekhā, candralekhā, vidyullekhā, vidyunmata.
Group of śikhā tantras: bhairavī, vīṇā, vīṇāmaṇi, sammoha, ḍāmara, atharvaṇa, kabandha, śiraccheda.