Bhaiṣajyaguru (Sanskrit: भैषज्यगुरु, Chinese: 藥師佛, Japanese: 薬師仏, Korean: 약사불, Vietnamese: Dược Sư Phật, Standard Tibetan: སངས་རྒྱས་སྨན་བླ), or Bhaishajyaguru, formally Bhaiṣajya-guru-vaiḍūrya-prabha-rāja ("Medicine Master and King of Lapis Lazuli Light"; Chinese: 藥師琉璃光(王)如來, Japanese: 薬師瑠璃光如来, Korean: 약사유리광여래, Vietnamese: Dược Sư Lưu Ly Quang Vương Như Lai), is the Buddha of healing and medicine in Mahāyāna Buddhism. Commonly referred to as the "Medicine Buddha", he is described as a doctor who cures suffering (Pali/Sanskrit: dukkha/duḥkha) using the medicine of his teachings.

The image of Bhaiṣajyaguru is usually expressed with a canonical Buddha-like form holding a gallipot and, in some versions, possessing blue or deep green skin. Though also considered to be a guardian of the East, in most cases, Akshobhya is given that role. As an exceptional case, the honzon of Mount Kōya's Kongōbu-ji was changed from Akshobhya to Bhaiṣajyaguru.

Bhaiṣajyaguru is described in the eponymous Bhaiṣajya-guru-vaiḍūrya-prabha-rāja Sūtra, commonly called the Medicine Buddha Sūtra, as a Bodhisattva who made twelve (12) great vows. His name is generally translated as "Medicine Guru, King of Lapis Lazuli Light". "Vaiḍūrya" is a precious stone which most translators have rendered as lapis lazuli. Librarian Marianne Winder has proposed that "vaiḍūrya" originally meant beryl; however, pure beryl is colorless, while its blue variant, aquamarine, is described as a 'precious blue-green color-of-sea-water stone' rather than the usual dark blue attributed to Bhaiṣajyaguru. While there is a dark blue variety of aquamarine called maxixe (pronounced mah-she-she), it is a New World gemstone—found primarily at the Maxixe Mine in the Piauí Valley near Itinga, Minas Gerais, Brazil—and was not known before 1917.

On achieving Buddhahood, Bhaiṣajyaguru became the Buddha of the eastern pure land of Vaiḍūryanirbhāsa "Pure Lapis Lazuli". There, he is attended to by two Bodhisattvas symbolizing the light of the sun and the light of the moon respectively:

The Tang Chinese Buddhist monk Xuanzang visited a Mahāsāṃghika monastery at Bamiyan, Afghanistan, in the 7th century CE, and the site of this monastery has been rediscovered by archaeologists. Birchbark manuscript fragments from several Mahāyāna sūtras have been discovered at the site, including the Bhaiṣajya-guru-vaidūrya-prabha-rāja Sūtra (MS 2385).

A Sanskrit manuscript of the Bhaiṣajya-guru-vaiḍūrya-prabha-rāja Sūtra was among the texts attesting to the popularity of Bhaiṣajyaguru in the ancient northwest Indian kingdom of Gandhāra. The manuscripts in this find are dated before the 7th century, and are written in the upright Gupta script.

The twelve vows of Medicine Buddha upon attaining Enlightenment, according to the Medicine Buddha Sūtra are:

Bhaiṣajyaguru is typically depicted seated, wearing the three robes of a Buddhist monk, holding a lapis-colored jar of medicine nectar in his left hand and the right hand resting on his right knee, holding the stem of the Aruna fruit or Myrobalan between thumb and forefinger. In the sūtra, he is also described by his aura of lapis lazuli-colored light. In Chinese depictions, he is sometimes holding a pagoda, symbolising the ten thousand Buddhas of the three periods of time. He is also depicted standing on a Northern Wei stele from approximately 500 CE now housed in the Metropolitan Museum of Art, accompanied by his two attendants, Sūryaprabha and Candraprabha. Within the halo are depicted the Seven Bhaiṣajyaguru Buddhas and seven apsaras.