Sharia (Arabic, “the way”), a term that refers to the body of laws and rules that regulate Muslim life. These laws are an expression of God’s will, according to Muslim belief, although derivation and application of the laws depend on interpretation by jurists-that is, leaders versed in Islamic law. Thus, while only one Sharia exists, it is expressed in legal interpretation, or fiqh, and there can be many schools of fiqh. Although some commandments are clearly enunciated in the Qur'an (Koran), the sacred text of Islam, jurists must derive most of them along the principles of a methodology known as the science of the law or usul al fiqh.

According to usul al fiqh, four principal sources (known as legal indicators) provide the basis for the Sharia: the Qur'an; the Sunnah, the collection of actions and sayings of the prophet Muhammad, the founder of Islam; ijma, meaning “consensus,” which for most jurists refers to the consensus over the centuries of the schools of law, but which may also refer to the consensus of the Muslim community; and qiyas, reasoning by analogy, in which jurists formulate new laws based on the Qur'an or the Sunnah.

Usul al fiqh will also, in addition to providing principles of interpretation, categorize the human actions that are covered by law. These actions may be wajib (obligatory), mandub (recommended), mubah (permissible), makruh (reprehensible), and haram (prohibited). Only violations of laws that belong to the first and last categories carry punishment under formal law; violations of laws in other categories are punishable only by God.

Over time, the laws that Muslims must follow have been elaborated upon by the schools of law. When the schools of law agree on a judgment, it becomes binding on Muslims. If the schools differ, their opinions are equally valid, providing they have followed the prescribed methodology. Today there are five schools of law, and their work is largely limited to applying laws and judgments passed in earlier times. These laws and judgments generally cover areas not legislated by the secular governments, chiefly family law and ritual. The most important debate among modern Muslims concern whether the Sharia should be applied in all aspects of life and whether and how to renovate it so that it addresses the most pressing issues facing the Muslim world today.