Indian Buddhist tantric tradition
Vajrayāna (; lit. 'vajra vehicle'), also known as Mantrayāna ('mantra vehicle'), Mantranāya ('path of mantra'), Guhyamantrayāna ('secret mantra vehicle'), Tantrayāna ('tantra vehicle'), Tantric Buddhism, and Esoteric Buddhism, is a Buddhist tradition of tantric practice that developed in Medieval India. Tantrism, which originated within Hinduism during the first millennium CE, significantly influenced South Asian Mahāyāna Buddhism, giving rise to distinct Buddhist tantric traditions. Emerging in the 7th century CE, these traditions spread across Southeast, East, and Central Asia, leading to distinct East Asian and Tibetan practices.
Vajrayāna practices are connected to specific lineages in Buddhism, through the teachings of lineage holders. Others might generally refer to these texts as the Buddhist Tantras. It includes practices that make use of mantras, dharanis, mudras, mandalas and the visualization of deities and Buddhas.
According to contemporary historical scholarship, Vajrayāna practice originated in the tantric era of medieval India (c. the 5th century CE onwards). However, traditionally, the adherents and texts of Vajrayāna claim these teachings have been passed down by an unbroken lineage going back to the historical Buddha (c. the 5th century BCE) or to other mythical Buddhas and bodhisattvas (e.g. Vajrapani).
According to Vajrayāna scriptures, the term "Vajrayāna" refers to one of three vehicles or routes to enlightenment, the other two being the Śrāvakayāna (also known pejoratively as the "Hīnayāna") and "Mahāyāna" (a.k.a. "Pāramitāyāna").
There are several Buddhist tantric traditions that are currently practiced, including Tibetan Buddhism, Chinese Esoteric Buddhism, Shingon Buddhism and Newar Buddhism. Historically, there were also other esoteric Buddhist traditions, such as that of maritime Southeast Asia, which are no longer practiced today.
Terminology.
In India, the initial term was Mantranāya (Path of Mantras), and Mantrayāna (Mantra Vehicle). Later, other terms were adopted, like Vajrayāna.
In Tibetan Buddhism practiced in the Himalayan regions of India, Nepal, and Bhutan, Buddhist Tantra is most often termed "Vajrayāna" (Tib. རྡོ་རྗེ་ཐེག་པ་, "dorje tekpa", Wyl. "rdo rje theg pa") and "Secret mantra" (Skt. "Guhyamantra", Tib. གསང་སྔགས་, "sang ngak", Wyl. "gsang sngags"). The vajra is a mythical weapon associated with Indra which was said to be indestructible and unbreakable (like a diamond) and extremely powerful (like thunder). Thus, the term is variously translated as Diamond Vehicle, Thunderbolt Vehicle, Indestructible Vehicle and so on.
Chinese Esoteric Buddhism it is generally known by various terms such as "Zhēnyán" (Chinese: 真言, literally "true word", referring to mantra), "Tángmì" or "Hanmì" (唐密 - 漢密, "Tang Esotericism" or "Han Esotericism")", Mìzōng" (密宗, "Esoteric Sect") or "Mìjiao" (Chinese: 密教; Esoteric Teaching). The Chinese term "mì" 密 ("secret, esoteric") is a translation of the Sanskrit term "Guhya" ("secret, hidden, profound, abstruse").
In Japan, Buddhist esotericism is known as or by the term Shingon (a Japanese rendering of "Zhēnyán"), which also refers to a specific school of .
The term "Esoteric Buddhism" is first used by Western occultist writers, such as Helena Blavatsky and Alfred Percy Sinnett, to describe theosophical doctrines passed down from "supposedly initiated Buddhist masters."
History.
Mahasiddhas and the tantric movement.
Tantric Buddhism is associated with groups of wandering yogis called mahasiddhas in medieval India. According to Robert Thurman, these tantric figures thrived during the latter half of the first millennium CE. According to John Myrdhin Reynolds, the mahasiddhas date to the medieval period in North India and used methods that were radically different from those used in Buddhist monasteries, including practicing on charnel grounds.
Since the practice of Tantra focuses on the transformation of poisons into wisdom, the yogic circles came together in "tantric feasts", often in sacred sites ("pitha") and places ("ksetra") which included dancing, singing, consort practices and the ingestion of taboo substances like alcohol, urine, and meat. At least two of the mahasiddhas cited in the Buddhist literature are comparable with the Shaiva Nath saints (Gorakshanath and Matsyendranath) who practiced Hatha Yoga.
According to Schumann, a movement called "Sahaja-siddhi" developed in the 8th century in Bengal. It was dominated by long-haired, wandering mahasiddhas who openly challenged and ridiculed the Buddhist establishment. The mahasiddhas pursued "siddhis", magical powers such as flight and extrasensory perception as well as spiritual liberation.
Ronald M. Davidson states that
 ;templatestyles src="Template:Blockquote/styles.css" / ;Buddhist siddhas demonstrated the appropriation of an older sociological form—the independent sage/magician, who lived in a liminal zone on the borders between fields and forests. Their rites involved the conjunction of sexual practices and Buddhist mandala visualization with ritual accoutrements made from parts of the human body, so that control may be exercised over the forces hindering the natural abilities of the siddha to manipulate the cosmos at will. At their most extreme, siddhas also represented a defensive position within the Buddhist tradition, adopted and sustained for the purpose of aggressive engagement with the medieval culture of public violence. They reinforced their reputations for personal sanctity with rumors of the magical manipulation of various flavors of demonic females (dakini, yaksi, yogini), cemetery ghouls (vetala), and other things that go bump in the night. Operating on the margins of both monasteries and polite society, some adopted the behaviors associated with ghosts (preta, pisaca), not only as a religious praxis but also as an extension of their implied threats. 
Tantras.
Tantrism originated within Hinduism and significantly influenced early South Asian Mahāyāna Buddhist practices, contributing to the emergence of unique Buddhist tantric traditions. These Buddhist tantric traditions, which developed in the 7th century CE, spread quickly across Southeast, East, and Central Asia, resulting in the formation of various distinct traditions in East Asia and Tibet.
There are other Mahāyāna sutras which contain "proto-tantric" material such as the "Gandavyuha" and the "Dasabhumika" which might have served as a central source of visual imagery for Tantric texts. Later Mahāyāna texts like the "Kāraṇḍavyūha Sūtra" (c. 4th–5th century CE) expound the use of mantras such as Om mani padme hum, associated with vastly powerful beings like Avalokiteshvara. The popular Heart Sutra also includes a mantra.
Vajrayāna Buddhists developed a large corpus of texts called the Buddhist Tantras, some of which can be traced to at least the 7th century CE but might be older. The dating of the tantras is "a difficult, indeed an impossible task" according to David Snellgrove.
Some of the earliest of these texts, Kriya tantras such as the "Mañjuśrī-mūla-kalpa" (c. 6th century), teach the use of mantras and dharanis for mostly worldly ends including curing illness, controlling the weather and generating wealth. The "Tattvasaṃgraha Tantra" ("Compendium of Principles"), classed as a "Yoga tantra", is one of the first Buddhist tantras which focuses on liberation as opposed to worldly goals. In another early tantra, the "Vajrasekhara" (Vajra Peak), the influential schema of the five Buddha families is developed. Other early tantras include the "Mahāvairocana Abhisaṃbodhi" and the "Guhyasamāja" (Gathering of Secrets).
The Guhyasamāja is a Mahayoga class of Tantra, which features forms of ritual practice considered "left-hand" ("vamachara") such as the use of taboo substances like alcohol, consort practices, and charnel ground practices which evoke wrathful deities. Ryujun Tajima divides the tantras into those which were "a development of Mahāyānist thought" and those "formed in a rather popular mould toward the end of the eighth century and declining into the esoterism of the left", this "left esoterism" mainly refers to the Yogini tantras and later works associated with wandering yogis. This practice survives in Tibetan Buddhism, but it is rare for this to be done with an actual person. It is more common for a yogi or yogini to use an imagined consort (a buddhist tantric deity, i.e. a yidam).
These later tantras such as the "Hevajra Tantra" and the "Chakrasamvara" are classed as "Yogini tantras" and represent the final form of development of Indian Buddhist tantras in the ninth and tenth centuries. The "Kalachakra tantra" developed in the 10th century. It is farthest removed from the earlier Buddhist traditions, and incorporates concepts of messianism and astrology not present elsewhere in Buddhist literature.
According to Ronald M. Davidson, the rise of Tantric Buddhism was a response to the feudal structure of Indian society in the early medieval period (ca. 500–1200 CE) which saw kings being divinized as manifestations of gods. Likewise, tantric yogis reconfigured their practice through the metaphor of being consecrated ("abhiśeka") as the overlord ("rājādhirāja") of a mandala palace of divine vassals, an imperial metaphor symbolizing kingly fortresses and their political power.
Relationship to Shaivism.
The question of the origins of early Vajrayāna has been taken up by various scholars. David Seyfort Ruegg has suggested that Buddhist tantra employed various elements of a “pan-Indian religious substrate” which is not specifically Buddhist, Shaiva or Vaishnava.
According to Alexis Sanderson, various classes of Vajrayāna literature developed as a result of royal courts sponsoring both Buddhism and Shaivism. The relationship between the two systems can be seen in texts like the "Mañjusrimulakalpa", which later came to be classified under Kriya tantra, and states that mantras taught in the Shaiva, Garuda and Vaishnava tantras will be effective if applied by Buddhists since they were all taught originally by Manjushri.
Sanderson notes that the Vajrayāna Yogini tantras draw extensively from the material also present in Shaiva Bhairava tantras classified as "Vidyapitha". Sanderson's comparison of them shows similarity in "ritual procedures, style of observance, deities, mantras, mandalas, ritual dress, Kapalika accouterments like skull bowls, specialized terminology, secret gestures, and secret jargons. There is even direct borrowing of passages from Shaiva texts." Sanderson gives numerous examples such as the "Guhyasiddhi" of Padmavajra, a work associated with the Guhyasamaja tradition, which prescribes acting as a Shaiva guru and initiating members into Saiva Siddhanta scriptures and mandalas. Sanderson says that the Samvara tantra texts adopted the pitha list from the Shaiva text "Tantrasadbhāva", introducing a copying error where a deity was mistaken for a place.
Ronald M. Davidson meanwhile, argues that Sanderson's arguments for direct influence from Shaiva "Vidyapitha" texts are problematic because "the chronology of the "Vidyapitha" tantras is by no means so well established" and that "the available evidence suggests that received Saiva tantras come into evidence sometime in the ninth to tenth centuries with their affirmation by scholars like Abhinavagupta (c. 1000 c.e.)" Davidson also notes that the list of pithas or sacred places "are certainly not particularly Buddhist, nor are they uniquely Kapalika venues, despite their presence in lists employed by both traditions." Davidson further adds that like the Buddhists, the Shaiva tradition was also involved in the appropriation of Hindu and non-Hindu deities, texts and traditions, an example being "village or tribal divinities like Tumburu".
Davidson adds that Buddhists and Kapalikas as well as other ascetics (possibly Pasupatas) mingled and discussed their paths at various pilgrimage places and that there were conversions between the different groups. Thus he concludes:
The Buddhist-Kapalika connection is more complex than a simple process of religious imitation and textual appropriation. There can be no question that the Buddhist tantras were heavily influenced by Kapalika and other Saiva movements, but the influence was apparently mutual. Perhaps a more nuanced model would be that the various lines of transmission were locally flourishing and that in some areas they interacted, while in others they maintained concerted hostility. Thus the influence was both sustained and reciprocal, even in those places where Buddhist and Kapalika siddhas were in extreme antagonism.
Davidson also argues for the influence of non-Brahmanical and outcaste tribal religions and their feminine deities (such as Parnasabari and Janguli).
Traditional legends.
According to several Buddhist tantras as well as traditional Tibetan Buddhist sources, the tantras and the Vajrayana was taught by the Buddha Shakyamuni, but only to some individuals. There are several stories and versions of how the tantras were disseminated. The "Jñana Tilaka Tantra", for example, has the Buddha state that the tantras will be explained by the bodhisattva Vajrapani. One of the most famous legends is that of king Indrabhuti (also known as King Ja) of Oddiyana (a figure related to Vajrapani, in some cases said to be an emanation of him).
Other accounts attribute the revelation of Buddhist tantras to Padmasambhava, saying that he was an emanation of Amitabha and Avalokiteshvara and that his arrival was predicted by the Buddha. Some accounts also maintain Padmasambhava is a direct reincarnation of Buddha Shakyamuni.
Philosophical background.
According to Alex Wayman, the philosophical view of the Vajrayana is based on Mahayana Buddhist philosophy, mainly the Madhyamaka and Yogacara schools. The major difference seen by Vajrayana thinkers is the superiority of Tantric methods, which provide a faster vehicle to liberation and contain many more skillful means ("upaya").
The importance of the theory of emptiness is central to the Tantric Buddhist view and practice. The Buddhist emptiness view sees the world