The Hare Krishna mantra, also referred to reverentially as the Maha Mantra ("Great Mantra"), is a sixteen-word Vaishnava mantra made well known outside of India by the International Society for Krishna Consciousness (commonly known as 'the Hare Krishnas'). This mantra appears within many traditions of Hinduism and is believed by practitioners to bring about a higher state of consciousness when heard, spoken, meditated upon, or sung out loud. According to Gaudiya Vaishnava theology, this higher consciousness takes the form of pure love of God (Krishna). The mantra is contained in the texts of Hinduism known as the Upanishads, which are considered by some scholars to have roots in the Vedic past.
In the hymn Vishnu Sahasranama spoken by Bhishma in praise of Krishna after the Kurukshetra war, he is also called Rama. "Hare" can be interpreted as either the vocative of Hari, another name of Vishnu meaning "he who removes illusion", or as the vocative of Harā, a name of Rādhā, Krishna's eternal consort or Shakti. According to A. C. Bhaktivedanta Swami Prabhupada, Harā refers to "the energy of God" while Krishna and Rama refer to God himself, meaning "He who is All-Attractive" and "He who is the Source of All Pleasure". Rama can also refer to Radha-Raman, another name of Krishna meaning beloved of Radha, or as a shortened form of Balarama, Krishna's first expansion.
The mantra is first attested in the (Kali Santarana Upanishad), a Vaishnava Upanishad associated with the Krishna Yajurveda. In this Upanishad, Narada is instructed by Brahma (in the translation of K. N. Aiyar):
Narada asks to be told this name of Narayana, and Brahma replies:
The mantra was popularized by Chaitanya Mahaprabhu roughly around 1500 CE when he began his mission to spread this mantra publicly to 'every town and village' in the world, travelling throughout India, and especially within the areas of Bengal and Orissa. Some versions of the Kali Santarana Upanishad give the mantra with Hare Rama preceding Hare Krishna, and others with Hare Krishna preceding Hare Rama (as quoted above). The latter format is by far the more common within the Vaishnava traditions, within which it is a common belief that the mantra is equally potent when spoken in either order.
In the 1960s an elderly monk known as A.C. Bhaktivedanta Swami Prabhupada, on the order of his guru, Srila Bhaktisiddhanta Sarasvati Thakura, brought the teachings of Sri Chaitanya from India and single-handedly took the responsibility of spreading them around the Western world. Beginning in New York, he encircled the globe fourteen times in the final eleven years of his life, thus making 'Hare Krishna' a well-known phrase in many parts of the world.
From a theological perspective, Hare Krishna devotees are classified as practitioners of Bhakti Yoga. They are also referred to as Gaudiya Vaishnavas because they follow a line of gurus descending from Chaitanya Mahaprabhu, who appeared in Bengal (Gauda is an old name of Bengal). Vaishnavism comes under the general banner of being a Hindu religion.
In terms of general diet among Gaudiya Vaishnavas, onions, garlic, and mushrooms are also generally avoided due to their purportedly adverse effects on the consciousness of the eater.
The Hare Krishna Movement was the subject of a number of academic studies. Today it is accepted by the academics as "the most genuinely Hindu of all the many Indian movements in the West". Not only Hindus or brahmanas were instrumental in the early appearance and spread of Hare Krishna movement in the 16th century. Haridasa Thakura, for example, was born outside of Hindu tradition but is considered the most famous convert of Chaitanya Mahaprabhu, apart from Rupa Goswami and Sanatana Goswami themselves, and the story of his heroism in the face of torture is told in Chaitanya Charitamrta, Antya lila.