What's the Differences Between the Sunni and Shia Sects of Islam?

The difference between Sunni and Shia sects of Islam do not exist to the dramatic degree many Western's assume. While there are slight variations in the way they view their religious leaders and attach meaning to the history of Muhammad’s family, cultural and political differences hold the most divisive power. Both sects emphasize the Five Pillars of Islam, read the same Quran, and consider each other Muslims.
The split between these two significant sects of Islam can be traced back to the 600s, soon after Muhammed’s death in 632. Muhammed’s son-in-law, Ali, gained support as the inheritor of the duty to spread Islam. Thus, "Shia" is an abbreviation of "Shiat Ali," or the people of Ali. Not all Muslims believed in Ali’s place as a leader. Yet this group respected Muhammed’s relative as a holy man. He was not a Messiah, as there is only one Messiah. Rather, the Shi’ites regarded him as the first in a series of Imam, or the direct descendents of Muhammad who act as messengers of God. There were 12 Imams before the bloodline died out in the 800s. Each of these Imams now has subsects devoted to their worship within Shia Islam. Shi’ites comprise 10-15% of all Muslims as the second largest sect, but that number is higher in certain countries such as Iran.
The majority of Muslims are Sunni, the largest and more orthodox sect of Islam. Sunnis do not attach any special power to the Imam, but have a rather less structured hierarchy of religious leaders. Some have compared their system as similar in spirit to Protestantism, where ministers are important advisers and community leaders, but they are neither infallible nor chosen by God. These leaders, called Caliphs, teach Islam. They bring peace, dignity, and goodwill to their members and encourage following the laws and guidelines laid out in the Quran. Also, they do not rule the place of worship in the sense of excluding other kinds of Muslims. All mosques are nondenominational, and can receive prayers from any sect.
Some exaggerated differences between Sunnis and Shi’ites are their organization of community religious leaders and their method of prayer. It’s true that Shi’ites focus more on the torment of martyrdom suffered by the Imams, and voluntarily submit to physical pain in order to sympathize with them. Yet Sunnis, too, respect the martyrs. Also, Shi’ites might combine the five daily prayers into three or four, if they work long hours, but this does not necessarily indicate a lesser amount of devotion. Since their respective country’s government does not always distribute funds in a way Shi’ites agree with, they might pay their zakat (a form of alms or tithing) directly to the poor, while Sunnis pay to the state. It’s largely apocryphal that Shi’ites promote a temporary marriage known as muttah for men travelling far from home, as this would run counter to the obligation of chastity.