There are two main sects in Islam: Sunni and Shi'ite. Sunni Islam is the largest denomination, although in some countries it is a minority.
Sunnis have their historical roots in the majority group who followed Abu Bakr, an effective leader, as Mohammed's successor, instead of his cousin and son-in-law Ali. The Sunnis are so named because they believe themselves to follow the sunnah or "custom" of the Prophet. Shi'ites are those Muslims who followed Ali, the closest relative of Mohammed, as Mohammed's successor.
Sufi Islam is not exactly a sect, but the mystical expression of Islam. It is therefore not included in the chart below. Sufism might be compared to Christian monasticism, in that both emphasize a quiet, simple life focused on obeying and experiencing God. Opinions of Sufis differ within the Muslim community.
The following chart compares the similarities and differences between the major Islamic sects. Please note that, as with all charts of this kind, information is generalized and should not be used as the only basis of information.