What Does It Mean to Be Mormon?

There are 6 million Mormons living in America, and Mormonism is one of the fastest-growing religions on the planet, with more than 12 million believers worldwide.

Later today Republican presidential contender Mitt Romney will make a speech publicly defending his Mormon faith. This morning, in anticipation of the former Massachusetts governor's speech, ABC News correspondent Dan Harris answered some common questions on "Good Morning America" about what it means to be Mormon.

Who was Joseph Smith?

He was the founder of Mormonism. In 1820, at age 14, Smith claimed that God and Jesus visited him near his home in upstate New York. Smith said he was restoring the true Church of Jesus Christ, a claim that angered a lot of Christians. He was killed by an angry mob.

Are Mormons Christian?

Mormons argue, emphatically, yes. But there are many real differences: Mormons believe that the Book of Mormon, which Joseph Smith claimed to have translated from golden plates he found near his home, is equally as holy as the New and Old Testaments. They also believe that God is a man of flesh and bone and has a wife, and that Jesus will return not only to Jerusalem, but also to Missouri.

How do Mormons treat minorities and women?

Until 1978 black men were not able to join the priesthood. Women are still not allowed to do so.

Why don't Mormons drink alcohol or coffee? They don't believe in artificial stimulants. Mormons are believers in clean living.

"When we went to an official church event recently, we were asked to sign this paper promising not to smoke or drink on church premises," said Harris.

Do they practice polygamy?

Many Americans are familiar with the polygamists on HBO's "Big Love," but the people who engage in plural marriage now are generally members of splinter groups. The mainline Mormon church outlawed polygamy in 1890.

The Mormon church has gone through an extraordinary transformation since its early days as a renegade religion. Today, it is very much in the mainstream. The Mormon Tabernacle Choir performs at presidential inaugurations. There are 10 Mormons in Congress and plenty of Mormon celebrities, including Gladys Knight and Donnie and Marie Osmond.