structural:expansion, stylistic:style_transfer, structural:summarization, structural:reformatting, information:extraction
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).