Indian Buddhism was dealt the coup de grâce by the armies of the Prophet Muhammad between the 10th and the 13th centuries AD, and had indeed been in decline for a long time before that. However, for more than a millenium after the Buddha's Parinirvâna it was very active in India.

The major features of Indian Buddhism can be broken down as follows:

1. The establishment of the Word of Buddha (Buddhavacana) as an oral tradition: its much later commitment to writing.
   
2. The holding of various councils or assemblies of the Sangha, some of which may be apocryphal.

These were:

Around AD, a highly significant new wave of development began to assert itself within the liberal spiritual tradition of Buddhism: Mahâyâna (Great Vehicle) in contrast to the older school of Hînayâna (Lesser Vehicle). The Mahâyâna represented a great creative flowering of various potentials that had hitherto lain latent in the Buddha's basic teachings. Various influences from southern India, the North-West and even Iran and the Mediterranean world formed Mahâyâna. The main trends are the following:

A new type of spiritual hero emerges who not seeks release from the painful rebirth cycle by himself like Arhats and the Pratyeka Buddha but would rather assist others (Bodhicitta: Wisdom-heart). The aspiring Bodhisattva practices "Six Perfections" (pâramitâ): giving, morality, patience, vigour, meditation and wisdom. He also passes through ten stages (bhûmi) on his way to Buddhahood. The first six stages correspond to pâramitâ. The higher four stages bring him to the level of celestial Bodhisattvas of the class like Avalokiteshvara or Manjushri. At the same time compassion (karunâ) was elevated together with wisdom (prajnâ) to be the ultimate virtues. Buddhist compassion has connotations of being able to feel the suffering of others as if they were one's own. Skill in means (upâya) is also emphasised.

As heirs to the Mahâsanhikas the Mahâyânas play down the role of the historical Buddha to be replaced by a transcendental principle which has manifested over untold aeons in innumerable forms and in innumerable places. Various mythical Buddhas emerged like Amitâbha, the Buddha of Infinite Light who resides in the western paridise (Sukhâvatî) where followers of the "Pure Land Sect" hope to merit rebirth.

As a development of pre-existing notions, the Mahâyâna accorded the Buddha three bodies (Trikâya Doctrine):

1. Nirmânakâya: his body of "transformation" in which he appears to the world to salvage the suffering;
2. Dharmakâya: wherein he is one with the eternal Dharma that lies beyond all dualities and conceptions;
3. Sambhogakâya: his "Bliss" body that appears to Bodhisatvas in the celestial realm where they commune with the Truth of Mahâyåna.

It becomes now possible to direct prayers (pûjâ: similar to bhakti cults in Hinduism) to Bodhisattvas instead of intensive personal effort to achieve spiritual progress. The laity becomes more important and plays an additional role to the traditional monastic order which still plays the central role in Buddhism. A new Mahâyâna-Sûtra, the Vimalakîrtinirdésa centres around an enlightened householder.

At the core of Mahâyâna philosophy lies the notion of Emptiness: Shûnyatâ, the absence of any kind of enduring or self-sustaining existence. This is very much in line with Buddha's original anâtman. Another term is tathatâ: "thusness" or "suchness" which signifies Emptiness in its immanent aspect. Buddha is sometimes called Tathâgata (He who is thus gone). The Tathâgata-garbha (garbha=germ) doctrine, on the other hand, proposes the doctrine of an immanent Absolute: the manifestation in form of a transcendental principle.

The structure of our everydays language doesn't allow us to describe things as they really are. It carves the world up into separate bits and pieces and so distorts reality which is not in itself fragmented in that way. Therefore Mahâyâna-Buddhism developed the principle of the two truths:

1. Conventional Truth: everyday's common-sense truth, basically distorted but open to skillful manipulation;
2. Absolute Truth: the things as they really are: empty and beyond thought and description. In terms of the Absolute Truth Nirvâna and Samsâra are identical.

The new Mahâyâna ideas are put down in a set of new Sûtras, one of the most magnificent outbursts of human history which took about five centuries. They are usually longer and more mystical and poetic, encrusted with rich imagenary than their counterparts in the original Pali-Canon. The Saddharma-Pundarîka (White Lotus of the true Dharma), the Vimalakîrtinirdésa (Exposition of Vimalakîrti) and the vast Prajnâpâramitâ (Perfection of Wisdom) are examples of these new Sûtras.

But, Mahâyâna and Hinayâna followers had still many aspects in common: they practice the same Vinaya, recognise the same five categories of faults and are attached to the same "Four Noble Truths". The Hinayâna followers remained the majority until the 8th century. An unsystematic phase of Mahâyâna development existed from 100 BC to 500 AD and the systematic phase started after 150 AD. The systematic phase saw the emergence of two schools: the Mâdhyamîka and the Yogâcâra. For the followers of Mâdhyamîka "wisdom" is most important while for the followers of Yogâcâra "meditation and trance" is at the core.

The Mâdhyamîka (Mâdhya means middle: Middle Path) School was founded by the South Indian philosopher Nâgârjuna around 150 AD. His major work is the Mûla Mâdhyamîka-kârikâ which is based on Shûnyatâ and negates all dualities with a worldly and a higher truth. In the early 5th century the School subdivided into two sub-schools:

1. Prâsangika (founded by Buddhapâlita);
2. Svâtantrika (founded by Bhâvaviveka).

Asanga (c. 310-390) and his younger brother Vasubhandu (c. 320-400) founded in the 4th century the Yogâcâra or Vijnânavâda School. They took a more positive approach than the followers of Mâdhyamîka: all is mind or consciousness: hence their doctrine of citta-matra: "mind only": according to this view, the objects of this world do not exist per se but are created from and by mind. To explain how this is done, they put forward the idea of store consciousness (âlaya-vijnâna), a kind of collective unconsciousness in which the seeds of all potential phenomena are stored and from which they ceaselessly pour into manifestation.

Between the 3rd and 7th centuries AD Mahâyâna developed into the "third turning of the Wheel of Dharma": Tantra or Mantrayâna (Secret Mantra Vehicle) or Vajrayâna (Diamond Vehicle) was born. It is sometimes labelled "Esoteric Buddhism": Tantric scriptures are a fourth addition to the original three pitaka of Vinaya: Sûtra and Abhidharma. It is based on the Mâdhyamîka teaching of Shûnyatâ. Tantra transforms the gross body, speech and mind into those of a Buddha by specific practices in close relationship with a Guru: the special hero of Tantra is the Siddha or Adept (Master).

This brings us into the fields of Yoga which are related with Hindu Tantra (around Shiva together with his Shakti). Buddhist Tantra which emerged later mainly from Tibet (mainly the Gelugpa School) was heavily influenced by Hindu Tantra. Tantra involves a great deal of symbolism and ritual with the following Tantric phenomena:

1. Yidam: the tantric pantheon is composed of a phantasmagoria of incredible deities (male and female): some benign like Avalokiteshvara or Tara, others are fearsome like Mahâkâla, Yamântaka, Guhyasamâja and Chakrasamvâra: they are emanations of the supreme tantric Buddha: Vajradhâra or Âdi-Buddha.
2. Dhyâni-Buddhas: One tantric deity family is represented by the five Tathâgatas or Dhyâni-Buddhas: Vairocana, Akshobya, Ratnasambhava, Amithâba and Amoghasiddhi.
3. Mandala: It is a meditation aid, an sacred place. It is a model of the cosmos and of the total human being: macrocosm and microcosm: Mandala consists of a series of concentric precincts converging on a focal sanctum, guarded by a Yidam or some other potent form of Ultimate Reality.
4. Mantra: These are highly- compressed power-pack formulae, usually of Sanskrit origin (Om Mani Padme Hûm). Some verbal formulae called dhârani and paritta (blessings) were used since early Buddhist times.
5. Bîja (or Seed) Mantra: This is a consonant which embodies the heart essence of a particular tantric deity.
6. Mudrâ: Literally a "symbol": It is a ritual gesture of the hands imbued with deep symbolic significance.
7. Mahâmudrâ: "The Great Seal": it signifies more than the subjective realisation of Emptiness: it is the Buddha nature, the basic mind within all sentient beings.
8. Vajra (tib. Dorje) and Ghanta (bell): These are the most important sysmbols in Tantra: Vajra is derived from the thunderbolt of the Hindu God Indra: It symbolises "skillful means" and the diamond-like quality of Shûnyatâ - when "skillful means" are allied to wisdom, which is symbolised by the Ghanta. Other ritual objects include dagger (phurba), skull-cup, tigh-bone trumpet etc.

Generally Tantra is divided into four main categories:

1. Action Tantra (Kriyâtantra);
2. Performance Tantra (Caryâtantra);
3. Yoga Tantra (Yogatantra);
4. Supreme Tantra (Anuttarayogatantra).

The oldest school of Tibetan Buddhism, the Nyingma Pa opted for a sixfold classification: Inner Tantra and Outer Tantra: Outer Tantra represents Action, Performance and Yoga Tantra while the Inner Tantra replaces the Supreme Tantra by thee new categories: Mahâ Yoga; Anu Yoga and Ati Yoga. Highest Yoga Tantra is, in tantric eyes, the apogee of the Buddhist Path which cannot be achieved by anyone. Each person must, therefore, find his/her appropriate level. The Tibetans divided all Buddhist teachings into Sûtra and Tantra: Sûtra includes both Mahâyâna and Hinâyâna.

Everybody who practices Tantra should have attained a high degree of stability and concentration through samatha and a clear understanding of Emptiness. Those initiated into tantric cults have to uphold grave vows (Samaya). Each pupil (Chela) has got its Guru with a special compatibility between the two for an effective "dharmic connection". The Tantra Path is a quick way to Enlightenment, if the Highest Yoga Tantra is followed.

When the Chela is ready to begin serious practice, his Guru will initiate him/her into the Mandala of his chosen Yidam. Guru Yoga: develop faith into the Lama-guide. The ritual is known as Abhisheka, for instance the Kâlachakra Initiations. At the topmost level of Yoga Tantra, there are two main stages: the Generation Stage (Preparatory: to conjure the Yidam and Mandala out of primal emptiness of his mind to visualise the Yidam and to dissolve him back into Emptiness) and the Completion Stage (Full Buddhahood is achieved by special yogic means: the three-body configuration according to the three bodies of Mahâyâna-Buddhism (Nirmânakâya, Dharmakâya and Sambhogakâya) will be finally achieved). The most subtle body consists of fine channels called nadi along which a number of plexus points or chakras are disposed. A so-called "wind energy" circulates through this system, which is basically inseparable from consciousness, but in its most gross forms manifests passions like anger and lust. In the unregenerate individual, the nadi are knotted up, so the movement of the wind energy is vitiated. Using the virtuoso powers of concentration perfected by means of intensive practice at the Generation Stage, theTantric Yogi seeks to direct and dissolve the wind energy into the minute Bindu (droplet) situated in the heart chakra. If this is achieved, conceptual thought automatically and instanteneously ceases and what remains is nothing less than the primordial state itself: Mahâmudrâ.

Controversy surrounds Buddhist Tantra - and indeed seems to have done from the earliest times - on account of its apparently unconventional methods and symbolism. In a recent conservation, a western student was discussing the demise of Buddhism in India with a learned Bikkhu: "The reason can be summed up in one word", the Bikkhu said: "Islam?" entured the westener: "No - Tantra" came the reply.

A strong sexual, dualistic notation exists in Tantrism, derived from Hindu-Tantra. The masculine denotes the active force of "skillful means" (Upâya) and the feminine the passive quality of "wisdom" (Prajnâ). The four stages of relationship between men and women (looking, smiling, touching and physical union) are also used as analogies for the kind of relationship that are possible with one's choosen deity. As for sexual Yoga, there is a tradition that this may be practised in certain very special and closely controlled circumstances during the Completion Stage of highest Yoga Tantra - but only by advanced practitioners who have transcended egotism and generated perfect Bodhicitta.