esoteric Buddhist sect that has had a considerable following in Japan since its introduction from China in the 9th century. Shingon may be considered an attempt to reach the eternal wisdom of the Buddha that was not expressed in words and, thus, not in his public teaching. The sect believes that this wisdom may be developed and realized through special ritual means employing body, speech, and mind, such as the use of symbolical gestures (mudras), mystical syllables (dhāraṇī), and mental concentration (yoga). The whole is intended to arouse a sense of the pervading spiritual presence of the Buddha that lies inherent in all living things.

The principal scripture of the school is the Dainichi-kyō (Sanskrit: Mahāvairocana-sūtra, “The Great Sun Sūtra”), a late text known only in its Chinese version. The whole universe is conceived to be the body of the Buddha Mahāvairocana (the “Great Illuminator”). He has two aspects, known as the kongō-kai (“diamond world”) and the taizō-kai (“womb world”), each of which has its characteristic depiction in the mandala, the ritual diagram often painted on the Shingon altar. Entry into the mandala is called kanjō (Sanskrit: abhiṣekha), an initiation ceremony involving sprinkling with water.

Shingon esotericism is a part of Vajrayāna, or Tantric Buddhism, which spread in the 8th century from northeastern and northwestern India to Tibet and Java as well as to China and from there to Japan. In Japan, however, the doctrine was much modified and systematized by the great religious leader Kūkai, known posthumously as Kōbō Daishi.

Kōbō Daishi studied the doctrine in China under a Tantric master and returned to found the Kongōbu Temple monastic centre at Mount Koya, south of Kyōto, in 819; he later established the Tō Temple in Kyōto as the sect's headquarters. By the end of the Heian period, it was, like the other Heian-founded sect, the Tendai, both rich and powerful.

The genius of Kōbō Daishi lay in appropriating the philosophical insights of the Chinese version of the doctrine for his own worldview, which is set forth in his theory of the 10 stages of spiritual development. This scheme not only ranked all the major Buddhist schools according to what he considered their degree of insight but also included Hinduism, Confucianism, and Taoism. The Shingon school took a conciliatory attitude toward Shintō and provided the theoretical basis for a rapport with Ryōbu (Ryōbu Shintō) (“Two Aspects”) Shintō, a Shintō-Buddhist amalgamation.