Islam's legal penal order rests on four sources: the Qu'ran, the Sunna (traditions of the Prophet), Ijma' (consensus of Islamic jurists), and Qiyyas (analogy with the Qu'ran and Sunna drawn by jurists). All of the sources of law are based in divine decrees. The principle of legality derives from the perspective that only God and not man can presume to define good and evil. The scope of application of the legality principle in Islamic law is broad but varies with the offense. Seen as a whole, however, the Islamic criminal justice system balances the legality principle with degrees of judicial flexibility similar to that in modern western law. Crimes of Hudud (theft, fornication, false accusation of fornication, brigandage, drinking of wine, apostasy, and rebellion against the legitimate authority) are firmly based on a principle of legality, with precise determination of both crime and punishment yet with some judicial flexibility depending upon the intent of the accused and the quality of the evidence. Crimes of Quesas and Diyya (homicide and assault), although left to individuals and families to initiate prosecution, show their basis in the legality principle by being bound to specific procedures and appropriate penalties in the process of retribution or compensation. In the case of Ta'azir offenses, offenses left undetermined by religious law, allow a great deal of flexibility to the judge yet are implicitly tied to the general principle of legality. A total of 84 footnotes is provided.