MR. VANDEHEI: Mayor Giuliani, this question comes from Eric Taylor (sp) from California. He wants to know, what is the difference between a Sunni and a Shi'a Muslim?

MR. GIULIANI: The difference is the descendant of Mohammed. The Sunnis believe that Mohammed's -- the caliphate should be selected, and the Shi'ites believe that it should be by descent. And then, of course, there was a slaughter of Shi'ites in the early part of the history of Islam, and it has infected a lot of the history of Islam, which is really very unfortunate.

Per about.com though something a little more substantial that has to do with Muslim life TODAY!

Shia Muslims believe that the Imam is sinless by nature, and that his authority is infallible as it comes directly from God. Therefore, Shia Muslims often venerate the Imams as saints and perform pilgrimages to their tombs and shrines in the hopes of divine intercession. Sunni Muslims counter that there is no basis in Islam for a hereditary privileged class of spiritual leaders, and certainly no basis for the veneration or intercession of saints. Sunni Muslims contend that leadership of the community is not a birthright, but a trust that is earned and which may be given or taken away by the people themselves.

Shia Muslims also feel animosity towards some of the companions of the Prophet Muhammad, based on their positions and actions during the early years of discord about leadership in the community. Many of these companions (Abu Bakr, Umar, Aisha, etc.) have narrated traditions about the Prophet's life and spiritual practice. Shia Muslims reject these traditions (hadith) and do not base any of their religious practices on the testimony of these individuals. This naturally gives rise to some differences in religious practice between the two groups. These differences touch all detailed aspects of religious life: prayer, fasting, pilgrimage, etc.

Sunni Muslims make up the majority (85%) of Muslims all over the world. Significant populations of Shia Muslims can be found in Iran and Iraq, and large minority communities in Yemen, Bahrain, Syria, and Lebanon.

The difference is the descendant of Mohammed.

this is pretty much the source of the original split, which occured right after mohammed's death. there is nothing in the quoran which supports the shia position on this, or the inherent sainthood of imams either. as with the celibacy of priests, an item never mentioned in the new testament, it was made up years later, to provide support for an otherwise unsupportable position.