Sharia (alternatively Shariah) is the body of religious law governing the Sunni branch of Islam (the smaller Shiite branch of Islam uses a system of jurisprudence called Jafari). As the Sunni branch is by far the dominant branch of Islam, Sharia is often simply called "Islamic Law".
Islam draws no distinction between religious and secular life, and hence Sharia covers not only religious rituals and the administration of the faith, but every aspect of day-to-day life.
The authority of Sharia is drawn from two major and two lesser sources. The first major source is specific guidance laid down in the Qur'an, and the second source is the Sunnah, or the way that Muhammad (the founder of Islam) lived his life. (The narration and study of how Muhammad actually lived his life is called the Hadith.) A lesser source of authority is Qiyas, which is the extension by analogy of existing Sharia law to new situations. Finally Sharia law can be based on ijma, or consensus. Justification for this final approach is drawn from the Qur'an, where Muhammad states; "My nation cannot agree on an error."
The comprehensive nature of Sharia law is due to the belief that the law must provide all that is necessary for a person's spiritual and physical well-being. All possible actions of a muslim are divided (in principle) into five categories: obligatory, meritorious, permissible, reprehensible, and haram (forbidden). Fundamental to the obligations of every muslim are the Five Pillars of Islam.
Most countries of the Middle East and north Africa maintain a dual system of secular courts and Sharia courts, in which the Sharia courts mainly regulate marriage and inheritence. Saudi Arabia and Iran maintain only Sharia courts. Sharia is also used in Afghanistan, Sudan, and Libya. Some states in northern Nigeria have reintroduced Sharia courts.