The actual differences between the Sunni and Shia sects of Islam will probably not seem as dramatic as many non-Muslims presume. There are notable variations in the ways they view their religious leaders and attach meaning to the history of Muhammad's family, however. Cultural and political differences make up the most divisive issues separating the two groups today.
Origins of the Sunni - Shia Split
The split between these two significant sects of Islam can be traced back to the time soon after Muhammad's death in the year 632, and centered on who would succeed the Prophet and become the first Caliph, or leader. A friend and advisor of Muhammad, Abu Bakr, was eventually selected to fulfill this role. Those who accept this decision call themselves Sunni. This group makes up the more traditional, or orthodox, form of the religion.
Some refused to follow Abu Bakr, however, and believed that another man, Muhammad's son-in-law, Ali, was Muhammad's true choice to be first the Caliph. The term, "Shia," is a sort of abbreviated version of the Arabic Shiat Ali, which means, "followers of Ali." The Shiites regarded him as the first in a series of Imams, or high clerics, who were direct descendants of Muhammad and acted as messengers of God. There were 12 Imams before the bloodline died out in the 800s. Each now has sub-sects devoted to his worship within Shia Islam.
The majority of practicing Muslims today are Sunni; Shiites, by comparison, comprise between 10% and 20% of the world's Muslims. While this makes them the second largest Islamic sect, in certain countries, such as Iran and Iraq, Shiites are the majority. Other denominations also exist — including the Sufis, Ahmadis, and others — but make up much smaller portions of the total Islamic population.
Differences in Religious Leadership
One of the major contrasts between the Sunni and Shia sects involves religious leadership. Shiites believe that God directly selects their Imams. These high clerics wield significant political authority that often extends across national borders. Sunni Muslims, on the other hand, do not attach any special power to the clergy, and their religious leaders tend not to concern themselves as much with expansive political roles. Instead, they tend to take on more of a localized teaching role.
Differences in Modern Day Practices
Sunni and Shiite Muslims are summoned to prayer each day by different calls, and practice certain rituals in different ways. Worship practices also differ in terms of the scriptures, or hadith, that are acceptable to them. While Shiites generally only recognize hadith that are attributed to Muhammad's immediate family or to followers of Ali, Sunni Muslims take a broader view, and consider all hadith to be valid.
Shiites place a greater emphasis on the torment of martyrdom suffered by the Imams, and voluntarily submit themselves to physical pain in order to sympathize with them. They also frequently combine the five daily prayers into three or four, especially if they work long hours, and do not consider this to indicate a lesser amount of devotion. Sunnis typically disagree with both practices, and place a higher priority on strict adherence to orthodox practices. Another area of contention is that Shiites accept and permit men to establish temporary marriages, known as mutah. Though Sunnis historically accepted these as well, they abolished the practice long ago.
Cultural and Political Divisions
The modern geo-political situation has amplified the differences between the two sects, and in turn has increased tensions between them. As Islam spread to countries around the world, some individual Muslim nations have tended to embrace one denomination over the other. This means that the denomination often becomes a part of the national identity and culture of the country, sometimes resulting in the oppression of the other sect, as well as both internal and external political tensions.
While conflict hotspots often tend to stand out in the world media, however, they do not inherently represent the state of Islam as a whole. Both sects emphasize the Five Pillars of Islam, read the same Q'uran (Koran), and consider each other to be Muslims. Mosques are by definition, non-denominational, and though individual mosques may be more associated with members of a particular denomination, members of any sect are normally free to pray in any mosque.