Mongolians have always taken Buddhism of the Tibetan (Lamaist) variety wholeheartedly. Their minds were tamed by Tibetan lamas (monks) when the Mongolian empire was at its height, and warriors were coming to grips with the complexities of controlling a multicultural empire.
Kublai Khaan found himself with a court in which all philosophies of his empire were represented. Teachers of Islam, Taoism, Nestorian Christianity, Manicheism, Confucianism and Buddhism all congregated at court, offering advice in managing state affairs. It was a Tibetan, Phagpa, who turned the mind of the great khaan. Only two generations after Chinggis Khaan, the imperial court took to Buddhism and was persuaded that the energies at the command of the lamas were greater than those of the warriors and their gods.
It took centuries before Buddhism really took hold. In 1578, Altan Khaan, a descendant of Chinggis Khaan, met the Dalai Lama Sonam Gyatso and converted. (The 'yellow faith' is the Gelugpa or 'yellow hat' form of Tibetan Buddhism which was thenceforth encouraged.) The Dalai Lama issued new laws forbidding the sacrificial slaughter of women, slaves and animals as funeral offerings. He ordered that an image of Gombo (Mahakala) be worshipped in every ger.
Reincarnate lamas were also born in Mongolia, the most prominent being the Jebtzun Damba of the Khalkh Mongols, who usually lived at Da Khuree, the monastic ger encampment which grew to become Ulaanbaatar. The first Jebtzun Damba reincarnation was the great Zanabazar, sculptor and energetic diplomat. He had to yield ultimate secular authority to the emperor of China in 1691 as the power of the Manchu Qing dynasty reached its zenith. Many of the Manchu emperors were themselves devout Tibetan Buddhists, and their patronage ensured Buddhism flourished throughout Mongolia, with many Mongolian reincarnate lamas regularly visiting Beijing to bless the emperor.
As Buddhism became the heartfelt faith of the masses, the Jebtzun Damba reincarnations never lost their dream of Mongolian independence, and as soon as Qing China collapsed in 1911, the eighth Jebtzun Damba declared Mongolia's independence. He wielded sacred and secular power, as did the Dalai Lama in Tibet.
The Purge. When the revolution of 1921 brought the communists to power, an uneasy peace existed between Mongolia's monasteries and the government. The communists realised that they were not strong enough to take on the revered religious establishment, which in 1921 numbered 110,000 lamas (including young boys), or one-third of the male population, who lived in about 700 monasteries. (Currently, there are about 1000 lamas in 30 monasteries.)
In 1924, when the eighth Jebtzun Damba died, the communist government prevented a successor from being found. (Mongolians believe that a ninth Jebtzun Damba reincarnated at a later date among exiled Tibetans, including the Dalai Lama, in Dharamsala, India.) In 1929, some of the property and herds belonging to the monasteries were seized and redistributed. Arrests and executions came in 1932, but the government quickly backed off as rebellions broke out. However, harassment continued - young lamas were conscripted into the army, and it was forbidden to build new monasteries.
Arrests of high-ranking lamas resumed in 1935. In 1937, the bloody purge began in earnest. Choibalsan's secret police descended on the monasteries. Young students were spared, but it is estimated that over 17,000 monks of middle and high rank were arrested, and virtually none was ever heard from again. Presumably, they were either executed or died in Siberian labour camps. The monasteries were closed, ransacked and burned. Only four monasteries were preserved as museums of the 'feudal period' - but even these were damaged.
Besides ideology, the government had other reasons for wanting to eliminate the lamas. First of all, they didn't work, and the Russians were anxious to send Mongolian labourers to Siberia. Secondly, lamas were celibate, and Mongolia's population was either stable or declining, which ran counter to the Marxist goals of 'more people, more production'. Thirdly, the communists believed - with some justification - that the monasteries were backward and opposed to modernisation. Finally, the monasteries were the centre of political and economic power in the country, and the government didn't appreciate the competition.
Except at Gandan monastery in Ulaanbaatar - which was kept as a showcase temple to impress foreigners - all religious worship and ceremonies remained outlawed until 1990. It was then that the democracy movement took hold, and freedom of religion was restored. In the past few years, there has been a phenomenal revival of Buddhism (and other religions). This is most evident during the Dalai Lama's visits, when hundreds of thousands of people flock to be blessed. Monasteries have reopened, and even some ex-Communist Party officials have become lamas.

In Mongolia today, there is a significant minority of Sunni Muslims, constituting as much as 5% of the total population. Most of them are ethnic Kazaks who live primarily in the far western aimag of Bayan-Olgii (there is also a small Kazak community in and around Nalaikh, near Ulaanbaatar).

Nestorian Christianity was part of the Mongolian empire long before western missionaries arrived. These days, with poverty, unemployment, alcoholism, domestic violence and confusion in abundance, Christian missionaries, often from obscure fundamentalist sects, have been keenly seeking converts.
Mongolian authorities are wary of these missionaries, who sometimes come to the country under the pretext of teaching English. In Ulaanbaatar, there are now more than 30 non-Buddhist places of worship, including a new US$1 million Catholic Mission Centre.

Whether shamanism is actually a religion is open to debate (there is no divine being or book of teachings), but it is practiced by some Mongolians, mainly the Tsaatan, Darkhad, Uriankhai and Buryat in northern Mongoloia.
Shamanism centres on the shaman, a 'doctor' and priest - known as a boo if male and udgan if female. People become shamans through heredity, or following a sudden and prolonged period of sickness and apparitions.
The main purpose of a shaman is to cure illness caused by the soul straying from the body, accompany the soul of a dead person to the other world, and protect the clan and livestock from evil spirits. The major shamanist ceremony is the Great Sacrifice, often held on the third day of the lunar new year, when many animals are sacrificed to the gods.
Shamanism has coexisted comfortably with Buddhism. The most obvious example is the abundance of ovoos, the piles of stones or wood which you see on top of most hills and mountain passes in the countryside.

Mongolia & Tibet
The links between Mongolia and Tibet are old and deep. Once in a lifetime, every devout Buddhist Mongolian tries to reach the holy city of Lhasa on a pilgrimage, despite the hardship and distance. Mongolian Buddhists have translated hundreds of texts into Mongolian, and most of the Jebtzun Dambas were born in Tibet. The Tibetans in turn relied on various Mongolian tribes to sustain their power; when the British invaded Tibet in 1903, the Dalai Lama fled to Mongolia for safety and stayed there a few years.

Ganlin Horn
For centuries, Ganlin horns had been used by head monks throughout Mongolia to call, and exorcise, evil spirits (lkham). The horns, which are about 18cm long and had to be kept hidden because of their powers, are no longer used, but they continue to create controversy.
Mongolian Buddhists claim that in Tibet, the horn had to be made from the left thigh bone of a sacrificed 18-year-old unmarried female virgin, because the lkham (which is female) wouldn’t respond to a call using a bone from a male. However, in Mongolia, the bone was apparently made from the thigh bone of (male) Buddhist monks who were already dead.
Examples of the Ganlin horn are found at the National Museum of Mongolian History and Monastery-Museum of Chojin Lama, the Manzshir Khiid monastery near Ulaanbaatar, and the museum in Sainshand, the capital of Dornogov province.

Important Figures of Tibetan Buddhism
The following is a brief guide to some of the gods and goddesses of the Tibetan Buddhist pantheon. It is neither exhaustive nor scholarly, but it may help you recognise a few of the statues you encounter in the monasteries of Mongolia.
Padmasambhava - the 'lotus-born' Buddha - assisted in establishing Buddhism in Tibet in the 8th century. He is regarded by followers of Nyingmapa Buddhism as the second Buddha. He is also known as Guru Rimpoche.
Avalokitesvara - 'glorious gentle one' - one of the three great saviours or Bodhisattvas. He is the Bodhisattva of compassion and is often pictured with 11 heads and several pairs of arms. His Tibetan name is Chenresig. The Dalai Lama is considered an incarnation of Avalokitesvara.
Manjushri - the 'princely lord of wisdom' - is regarded as the first divine teacher of Buddhist doctrine. He is also known as Jampel.
Vajrapani - 'thunderbolt in hand' - is one of the three great saviours or Bodhisattvas. He is also known as Channadorje. The thunderbolt represents indestructibility and is a fundamental symbol of Tantric faith.
Sakyamuni - the 'historical' Buddha - born in Lumbini in the 6th century BC in what is now southern Nepal, he attained enlightenment under a pipal (Bo) tree, and his teachings set in motion the Buddhist faith. In Tibetan-style representations, he is always pictured sitting cross-legged on a lotus flower throne.
Maitreya - the 'Buddha of the future'. He is passing the life of a Bodhisattva and will return to earth in human form 4000 years after the disappearance of Sakyamuni Buddha.
Milarepa - a great Tibetan magician and poet who is believed to have attained the supreme enlightenment of buddhahood in the course of one life. He lived in the 11th century and travelled extensively throughout the Himalayan border lands. Most images of Milarepa picture him smiling, holding his hand to his ear as he sings.
Tara - 'the saviouress' - has 21 different manifestations. She symbolises fertility and is believed to be able to fulfil wishes. Statues of Tara usually represent Green Tara, who is associated with night, or White Tara, who is associated with day.
Gombo - the wrathful-looking god wields the flaming sword which severs all attachment. He is a common sight in the inner sanctums of temples. The oldest monastery in Mongolia, Erdene Zuu, is dedicated to Gombo.

Greenway, Paul, Storey, Robert & Lafitte, Gabriel, Lonely Planet - Mongolia, Second Edition, Lonely Planet Publications, Hawthorn, Australia, 1997, pp. 39-45.