It was founded in 622 CE by Mohammed the Prophet (circa 570 to 632 CE) in Medina. It is the youngest of the world's great religions. Followers of Islam are called Muslims. "Muslim" is an Arabic word that refers to a person who submits themselves to the Will of God. "Allah" is an Arabic word which means "the One True God." An alternate spelling for "Muslim" that is occasionally used is "Moslim"; it is not recommended because it is often pronounced "mawzlem": which sounds like an Arabic word for "oppressor". Some Western writers in the past have referred to Islam as "Mohammedism"; this is deeply offensive to many Muslims, as its usage can lead some to the concept that Mohammed the Prophet was in some way divine.

Little is known about Muhammad's childhood. He was orphaned at the age of 6 and brought up by his uncle. As a child, he worked as a shepherd. He was taken on a caravan to Syria by his uncle at the age of 9 (or perhaps 12). Later, as a youth, he was employed as a camel driver on the trade routes between Syria and Arabia. Mohammed later managed caravans on behalf of merchants. He met people of different religious beliefs on his travels, and was able to observe and learn about Judaism, Christianity and the indigenous Pagan religions.

After marriage, he was able to spend more time in meditation. At the age of 40, (610 CE), he was visited in Mecca by the angel Gabriel. He developed the conviction that he had been ordained a Prophet and given the task of converting his countrymen from their pagan, polytheistic beliefs and what he regarded as moral decadence, idolatry, hedonism and materialism.

He met considerable opposition to his teachings. In 622 CE he moved north to Medina due to increasing persecution. The trek is known as the hegira . Here he was disappointed by the rejection of his message by the Jews. Through military activity and political negotiation, Mohammed became the most powerful leader in Arabia, and Islam was firmly established in the area.

By 750 CE, Islam had expanded to China, India, along the Southern shore of the Mediterranean and into Spain. By 1550 they had reached Vienna. Wars resulted, expelling Muslims from Spain and Europe. Since their trading routes were mostly over land, they did not an develop extensive sea trade (as for example the English and Spaniards). As a result, the old world occupation of North America was left to Christians.

Believers are currently concentrated from the West coast of Africa to the Philippines. In Africa, in particular, they are increasing in numbers, largely at the expense of Christianity.

Many do not look upon Islam as a new religion. They feel that it is in reality the faith taught by the ancient Prophets, Abraham, David, Moses and Jesus. Mohammed's role as the last of the Prophets was to formalize and clarify the faith and to purify it by removing foreign ideas that had been added in error.

Estimates of the total number of Muslims in the world vary greatly:

• 0.700 billion or more, Barnes & Noble Encyclopedia 1993
• 0.817 billion, The Universal Almanac (1996)
• 0.951 billion, The Cambridge Factfinder (1993)
• 1.100 billion, The World Almanac (1997)
• 1.200 billion, CAIR (Council on American-Islamic relations)

At a level of 1.2 billion, they represent about 22% of the world's population. They are the second largest religion in the world; Christianity has 33%.

Islam is growing about 2.9% per year which is faster than the total world population which increases about 2.3% annually. It is thus attracting a progressively larger percentage of the world's population. The number of Muslims in North America is in dispute: estimates range from under 3 million to over 6 million. The main cause of the disagreement appears to be over how many Muslim immigrants have converted to Christianity since they arrived in the US. Statistics Canada reports that 253,260 Canadians identified themselves as Muslims (0.9% of the total population) during the 1991 census. Those figures are believed to be an under-estimate.