Two terms are used to refer to law in Islam: shariah and fiqh. Shariah refers to God's divine law as contained in the Quran and the sayings and doings of Muhammad (hadith). Fiqh refers to the scholarly efforts of jurists (fuqaha) to elaborate the details of shariah through investigation and debate. Muslims understand shariah to be an unchanging revelation, while fiqh, as a human endeavor, is open to debate, reinterpretation, and change.
Scholars and jurists developed the law by combining knowledge of the Quran, hadith, and analogical reasoning with local practice. Beginning in the mid-eighth century, the major Sunni schools of legal thought (madhhabs)—Hanafi, Maliki, Shafii, and Hanbali—and the Twelver Shii Jafari madhhab emerged. Other minor and short-lived schools also developed.
--from "Islamic Law." In The Oxford Dictionary of Islam, edited by John L. Esposito. Oxford Islamic Studies Online, http://www.oxfordislamicstudies.com/article/opr/t125/e1107 (accessed 15-Jul-2011).