Yidam is a type of deity associated with tantric or Vajrayana Buddhism said to be manifestations of Buddhahood or enlightened mind. During personal meditation (sādhana) practice, the yogi identifies their own form, attributes and mind with those of a yidam for the purpose of transformation. Yidam is sometimes translated by the terms “meditational deity” or “tutelary deity”. Examples of yidams include the meditation deities Chakrasamvara, Kalachakra, Hevajra, Yamantaka, and Vajrayogini, all of whom have a distinctive iconography, mandala, mantra, rites of invocation and practice.

In Vajrayana, the yidam is one of the three roots of the “inner” refuge formula and is also the key element of Deity yoga since the ‘deity’ in the yoga is the yidam.

Other enlightened beings such as the common forms of buddhas, bodhisattvas , Padmasambhava , some dharmapalas , wealth deities or yab-yum representations , among others, can also be used as Yidams .

The Yidams are both a specific form of a Buddha (concept) , as well as the basic or potential nature of the student to become a Buddha. The student meditates on the prominent characteristics of the Yidam until he achieves a complete union with it. The Yidam, which can be both masculine and feminine, can correspond to the personal buddhic aspect of the person practicing, the nature of the Yidam corresponds to the psychological temperament and qualities of each adept.

Avalokiteshvara (Tib. Chenrezig ), Tara , Manjushri and particularly Kalachakra , Hevajra and his consort Nairatmya or Heruka- Chakrasamvara and his consort Vajravarahi are often chosen as Yidams, but any buddha aspect of the pantheon of Tantric Buddhism ( Vajrayāna ) can be used .

The Yidam is used as a method of transformation towards complete enlightenment and according to some traditions it is considered emanation from the mind of the practicing person.

Yidam is said to be a contraction of Tib. yid-kyi-dam-tshig, meaning “samaya of mind”- in other words, the state of being indestructibly bonded with the inherently pure and liberated nature of mind.

The Sanskrit word iṣṭadevatā or iṣṭadevaḥ a compound of iṣṭa (desired, liked, reverenced) + devatā (a deity or divine being) is a term associated with yidam in many popular books on Buddhist Tantra but has not been attested in any Buddhist tantric text in Sanskrit.

Three Roots
The yidam appears as one of the Three Roots in the Tibetan Buddhist ‘Inner’ refuge formulation. The iconography of the yidam may be ‘peaceful’, ‘wrathful’ (Tibetan tro wa) or ‘neither peaceful or wrathful’ (Tibetan: shi ma tro), depending on the practitioner’s own nature. The yidam represents awakening and so its appearance reflects whatever is required by the practitioner in order to awaken. The guru will guide the student as to which yidam is appropriate for them and then initiation into the mandala of the Ishta-deva is given by the guru, so that Deity Yoga practices can be undertaken. In essence, the mindstream of the guru and the yidam are indivisible. The yidam is considered to be the root of success in the practice.

Buddhist Vajrayana Refuge Formulations
Outer (‘Triple Gem’) Buddha Dharma Sangha
Inner (‘Three Roots’) Guru Yidam Dharmapala and Dakini
Secret Nadi Prana Bindu
Ultimate Dharmakaya Sambhogakaya Nirmanakaya

In East Asian Buddhism
The Vajrayana traditions of China, Korea and Japan, while smaller and less prominent than Indo-Tibetan tantric Buddhism, are characterized in part by the utilization of yidams in meditation, though they use their own terms. One prominent ishta-devata in East Asian vajrayana is Marici (Ch: Molichitian, Jp: Marishi-ten). In the Shingon tradition of Japan, prominent yidam include the “five mysteries of Vajrasattva,” which are Vajrasattva (Jp. Kongosatta), Surata/Ishta-vajrinī (Jp. Yoku-kongonyo”慾金剛女”), Kelikilā-vajrinī (Jp. Shoku-kongonyo”触金剛女”), Kāmā/Rāga-vajrinī ((Jp. Ai-kongonyo”愛金剛女”), and Kāmesvarā/Mana-vajrinī ((Jp. Man-kongonyo”慢金剛女”).

Yidam in Nepalese Newar Buddhism
The principal yidam in the Newar Vajrayana tradition of Nepal are Chakrasamvara and Vajravarahi. In that tradition, three components are essential to a temple complex: a main shrine symbolizing Svayambhu Mahachaitya; an exoteric shrine featuring Buddha Shakyamuni and other buddhas and bodhisattvas; and an esoteric shrine dedicated to the yidam, to which only initiates may be admitted.

Through their long history and the interplay of mutual influences that ensued, Hinduism and Buddhism share many spiritual techniques and approaches. In this case, it was from Hinduism that meditation and devotion to a deity were reintroduced into Buddhism.

Here also the various deities are personifications of certain aspects of the ultimate reality called Brahman in the non-dual view , or of the God or the single Goddess, Ishvara or Mahādevī , in the multiple forms of Shiva , Vishnu , etc. Thus Ganesh , Shiva, Hanuman are gods very much in need in India.

Working definition
According to The Tonglen and Mind Training Site which discusses Tonglen and Ngöndro, Yidam is:

Visualized representative of your enlightened energy, or Buddha-nature. Tricky concept for Westerners; closest concept might be that of a patron saint in Catholicism, except that a yidam is not a historical figure and is not necessarily supposed to ‘exist’ in the same way human beings do. Other related concepts might be a totem or power animal in the Native American tradition, or even the fairy godmother in children’s tales.

A Yidam is an enlightened being with whom one identifies oneself during meditation: one perceives through this identification one’s own Buddha nature. The most famous Yidams have an angry, terrifying attitude: Hayagriva (wrathful manifestation of Avalokiteshvara ), Vajrakilaya (Dorje Phurba), Samputa , Guhyasamaja , Yamantaka , Hevajra , Kurukulle , Chakrasamvara , Vajrayogini and Kalachakra . Other enlightened beings such as the peaceful forms of Buddhas and Bodhisattvas like Padmasambhava andManjusri can also be practiced as Yidams.

Yidams are both a specific form of a Buddha and the inherent potential of each to become a Buddha. The student, after strong meditation, must visualize the main characteristics of his Yidam until he makes a complete union with him and makes it a “reality”. Subsequently the student must “deconstruct” this reality to understand that it is an illusion that has no existence in itself. The Yidam can be male or female, and refer to a personal deity whose nature corresponds to the student’s psychological temperament.

According to some traditions, the Yi-dam is considered as the emanation of the spirit (English: mind) of the adept. The Yi-dam is an appearance of the archetypal forces that represent, not the actual spiritual development of the individual, but the final phases of his spiritual development. These forces are in a way a preparatory instruction. The Yi-dam is absolutely not to be considered as a god (the gods part of samsara ). In authorized initiations, the Lama helps the practitioner to become aware of his own Yi-dam.

During the (meditation) practice of the generation stage, a practitioner (sadhaka) establishes a strong familiarity with the Ishta-deva (an enlightened being) by means of visualization and a high level of concentration. During the practice of the completion stage, a practitioner focusses on methods to actualize the transformation of one’s own mindstream and body into the meditation Deity by meditation and yogic techniques of energy-control such as kundalini (tummo in Tibetan). Through these complementary disciplines of generation and completion one increasingly perceives the pervasive Buddha nature.

Judith Simmer-Brown summarises:

… a yidam, a personal meditational deity, a potent ritual symbol simultaneously representing the mind of the guru and lineage of enlightened teachers, and the enlightened mind of the tantric practitioner. Recognizing the inseparability of these two is the ground of tantric practice.

Berzin (1997: unpaginated) in discussing Buddhist refuge commitment and bodhisattva vows frames a caution to sadhana:

More specifically, this commitment means not taking ultimate refuge in gods or spirits. Buddhism, particularly in its Tibetan form, often contains ritual ceremonies, or pujas, directed toward various Buddha-figures or fierce protectors in order to help dispel obstacles and accomplish constructive purposes. Performing these ceremonies provides conducive circumstances for negative potentials to ripen in trivial rather than major obstacles, and positive potentials to ripen sooner rather than later. If we have built up overwhelmingly negative potentials, however, these ceremonies are ineffective in averting difficulties. Therefore, propitiating gods, spirits, protectors or even Buddhas is never a substitute for attending to our karma – avoiding destructive conduct and acting in a constructive manner. Buddhism is not a spiritual path of protector-worship, or even Buddha-worship. The safe direction of the Buddhist path is working to become a Buddha ourselves.

In the Vajrayana practices of Tibetan Buddhism, ‘safe direction’, or ‘refuge’ is undertaken through the Three Roots, the practitioner relying on an Ishta-deva in Deity Yoga as a means of becoming a Buddha.

Common yidams
Some common yidams include Hayagriva, Vajrakilaya (Dorje Phurba), Samputa, Guhyasamaja, Yamantaka, Hevajra, Kurukulla, Cakrasamvara, Vajrayogini, and Kalachakra. Also, other enlightened beings such as the regular forms of the Buddhas, Bodhisattvas, Padmasambhava, certain Dharmapalas, Dakinis, Wealth Deities, and yab-yum representations, among others, can also be practiced as a yidam. Avalokiteshvara, Tara, Manjusri, Hevajra and consort Nairatmya, Heruka-Chakrasamvara and consort Vajravarahi, etc. are frequently chosen as yidams, but any deity of the tantric pantheon may be adopted as such. The yidam is used as a means or a goal of transformation towards full enlightenment. According to certain traditions, the Ishtadevas are considered as the emanation of the adept’s own mind.