Insha'allah, this is the first of a multi-part series I'm writing for Street Prophets on the different groups of Muslims worldwide. As time permits, current plans are to write diaries on the Shi'a and Sufis, the so-called Heretics, and various Islamic movements.
A few days ago, Ojibwa suggested to me, in his diary, Ardipithicus Ramidus, that "It might also be interesting to see a diary outlining the different kinds of Islam."
Now I found this suggestion a little strange, if only for its vagueness: "Different kinds of Islam?" To me there is only one Islam, but I suspect that what Ojibwa really wants to see is a diary on the different sects, if you will, among Muslims worldwide. I've never tackled this topic before; it's always seemed rather elementary a subject to me, but I can see where others might find this type of information of interest.
Generally speaking, the Muslim world can be divided into two primary groups: Sunnis and Shi'a. Most non-Muslims are aware of a third group, Sufis, but for Muslims, Sufis fit within the other two groups; i.e., a Sufi may be either a Sunni or a Shi'a. Becoming a Sufi doesn't mean you're excluded from either the Sunni or Shi'a traditions, although not all Sunnis approve of Sufi practices.
Sunnis are the majority group among Muslims, making up roughly 87-90% of all Muslims worldwide (according to the recently-released Pew Forum report on worldwide Muslim population figures). Sunnis believe in following the Qur'an and the Sunnah of the Prophet Muhammad (pbuh). The Sunnah is the words and actions of the Prophet (pbuh) recorded by the first several generations of Muslims. Most of the Sunnah comes in the form of ahadith (sing., hadith), which are anecdotes describing some incident that either the Prophet (pbuh) or one or more of his Companions (known collectively as the Sahabah) did. These ahadith were collected into multi-volume books by a number of scholars who graded what is known as the isnad of the hadith as to the hadith's reliability. (The isnad is the chain of transmitters of the hadith; i.e., who said what to who, from the first transmitter until the last when it was recorded into one of the collections.) Each person within the isnad was evaluated as to his or her memory, truthfulness, and a number of other factors. The isnad then received a grade as to its authenticity: authentic, fair, weak, fabricated, and shaky. There are six collections of ahadith in which virtually all of the ahadith are considered sahih or authentic, of which the two most important sahih collections are by Bukhari and Muslim. It should be noted that the actual anecdote (called the matn) is not graded in any way, only the isnad. Three of the six collections, plus a fourth that is not part of the six, can be found here.)
From an analysis of the Qur'an and Sunnah came to be developed a number of legal schools of thought. Four of these schools survive today, while a number of others have disappeared over time. The four surviving schools are all named after the respective scholars who started the school. (It should also be noted that none of these scholars actually sought to start a school of thought in their name; rather, the scholars attracted students who perpetuated their teachings.) The four schools are known as the Hanafi, Maliki, Shafi'i, and Hanbali madhahib (schools of thought).
Each of these schools tend to have a geographic predominance, although Sunnis are free to choose whichever madhhab (school of thought) they prefer. Hanafis are mostly located throughout Central and South Asia, the countries between Turkey and Jordan and Iraq, plus parts of Iran and the Balkans. Malikis are primarily in Western Africa, from the Atlantic to Libya. Shafi'i's are predominant along the east (Indian Ocean) coast of Africa, from Egypt on south, plus the countries of Yemen, the UAE, and all of southeast Asia (where I live). The Hanbali school is more or less only in Saudi Arabia.
From a practical perspective, the doctrinal differences between the four schools are minor. All four schools are considered to be "rightly guided," and there is no antagonism between any of the four. Muslims of any school, for example, may pray behind an imam (prayer leader) of another school. Yusuf al-Qaradawi, in his famous book, The Lawful and the Prohibited in Islam (which I happen to be reading right now), ignored doctrinal differences between the four schools on the various topics he discussed and, in fact, often provided examples of when one or more of the four schools would differ from each other on specific subjects. (For example, with respect to prohibited meats, the Malikis reject only those that are specifically mentioned in the Qur'an, whereas the other three schools prohibit other types of meats that are not mentioned in the Qur'an but were mentioned either directly or as part of a general classification (e.g., "birds with talons"; i.e., birds of prey) by the Prophet (pbuh).)