Mormonism's worldwide following is outgrowing its US roots , and it may become the first global religion to have emerged since Islam, writes Aengus Collins.

There may still be two years to go until the inauguration of the next US president, but the early stages of the race are well under way, with candidates already putting their names into the hat to succeed George W Bush.

Among the small group of men and women thought to have a realistic chance of winning is Mitt Romney. He is the recently departed Republican governor of Massachusetts, a successful consultant and banker, and the man who against all odds turned the beleaguered Salt Lake City Winter Olympics into a success five years ago. So far so good. But Mitt Romney is also a Mormon - a member of the Church of Jesus Christ of Latter-Day Saints. And the prospect of a presidential bid has Americans asking themselves, not for the first time, whether they would be willing to accept a man of that faith as their leader.

This is not a question that the Irish electorate is likely to be faced with any time soon, but there is a small community of Mormons in the Republic (numbers are greater in the North), and the colourful history of Mormon missionary activity in Ireland stretches right back to the mid-1800s, just 20 years after the religion was established.

Mormonism was established in New York in 1830 by Joseph Smith jnr (see panel). In 1820, when he was 14, Smith had had a vision in which he claimed to have been told by God and Jesus that he had been chosen to lead a restoration of the church on earth, to rescue it from the error or apostasy into which it had lapsed after the death of the first apostles. Smith then said he was visited by an angel named Moroni, who revealed to him a set of golden plates containing an account of Jesus's work on earth. Each year, Smith would visit the hill where the plates were located, but only in 1827 was he allowed by the angel to take the plates and translate their contents into English.

The result of his efforts was the Book of Mormon, which stands alongside the Bible (and a number of other texts by Smith and his successors as prophet-leader of the church) as a cornerstone of Mormon scripture. The Book of Mormon sets out God's dealings with the earliest inhabitants of the Americas, and tells among other things of Jesus visiting the continent after his resurrection and ascension, to minister to warring communities there and to usher in a period of peace.

Missionary activity is central to Mormonism and while much of the religion's early history was dominated by the troubled process of finding a welcoming home in America, its leaders sought to internationalise the faith from an early date. This can be seen from how quickly its representatives arrived in Ireland.

By 1846, the Mormons had settled in what is now Salt Lake City, Utah, where the religion's headquarters remain. Four years later, the first missionaries reached Dublin, led by Edward Sutherland. They were not particularly well received.

According to Brent Barlow, an American academic who has documented this period, Sutherland's first meeting drew several hundred irate attendees. Perhaps surprisingly, the greatest problems were not with the Catholic majority, but with Protestant students from Trinity College.

Sutherland wrote at the time: "We have had the attendance of several divinity students from Trinity College occasionally, but we should be surprised if they were to keep quiet . . . For several weeks past, they attended our week-night meetings for no other object but to prevent us worshipping in peace."

Sutherland's successor, Gilbert Clements, was bothered by the same Trinity contingent and was less circumspect in his 1853 account of his difficulties: "Of all the anti-Mormons I ever saw, and I have seen a great many, those of Dublin seem to be pre-eminently wicked."

After the Mormons in Utah had sent out their missionaries across the world, they began to receive immigrant converts travelling in the other direction. Here too there is an Irish connection, for among American Mormons, the Irish were notorious for their absence from this wave of immigration.

In 1905, the Philadelphia North American even published an article under the title "Why There Are No Irish Mormons".

It was an urban myth, however: there were Irish Mormons. But a convoluted story had taken root about Brigham Young (Joseph Smith's successor as church president and prophet) being duped by an Irishman named Branigan and decreeing as a result that no Irish people should be admitted to the church.

At present, there are around 3,000 Mormons in Ireland. There are still missionaries in the country - pairs of clean-cut young men in crisp, dark suits - but according to Alen O'Farrell, one of the church's leaders in the Dublin region, most of Mormonism's gradual growth here takes place on a word of mouth basis between family and friends.

For example, Brenda Fagan, another member of the church in Dublin, converted 25 years ago when she was 28, after her sister converted. She had been sent to talk to her sister by their concerned mother, but ended up gradually coming around to the idea of a restored church and the role of the religion's leader as a living prophet. Her parents subsequently converted too.

It is difficult to describe succinctly the points of similarity and difference between Mormonism and mainstream Christianity. On the one hand, the centrality of Jesus to each is a crucial point of similarity, which for day-to-day purposes, is sufficient to sustain a growing amount of inter-religious activity and dialogue, particularly involving evangelical Protestantism. But there are significant differences. For example, Mormonism takes a very different view about how the natures of man and God compare. Where mainstream Christianity would hold that the two are fundamentally different, for Mormons, the difference seems to be more one of degree or evolution: "As man is, God once was. As God is, man may become."

Beliefs differ too on original sin, on the nature of the Trinity, on baptism for the dead, and on the idea of continuing revelation through modern prophets. What is the sum total of these differences - is Mormonism a truly Christian religion?

Mormons tend to say yes, and Brenda Fagan and Alen O'Farrell certainly have no doubt that their religion is a deeply Christian one. But many others are inclined to disagree, and in 2001, the Vatican's Congregation for the Doctrine of the Faith ruled that Mormon baptisms are not valid.

"Historically," says Douglas Davies, a professor at Durham University, "Mormonism has to be seen as Christian. It has clearly Christian roots. But theologically, in terms of doctrine and philosophy, one can see why people would say it's not."

In a book published last year, American sociologist Rodney Stark repeated his oft-cited prediction that Mormonism is growing so fast it will soon become the first new global religion to have emerged since Islam. In 2004, there were 12 million Mormons around the world; Stark estimates that there could be as many as 268 million by 2080.

Already, the church's centre of gravity is shifting from its American heartlands, and Mormons in the US now form a minority of the religion's worldwide membership.

Stark, who is not himself a Mormon, suggests that the strikingly contemporary nature of Mormonism's prophetic tradition is particularly resonant in our modern world. We thrive on information and expect to know more about everything than previous generations, he says. Mormonism's belief in continuing revelation responds to that expectation more effectively than mainstream Christianity.

As Alen O'Farrell puts it: "We believe the Bible to be the word of God, but we don't believe that when the Bible was finished God stopped talking."