Legal pluralism is the existence of multiple legal systems within one (human) population and/or geographic area. Plural legal systems are particularly prevalent in former colonies, where the law of a former colonial authority may exist alongside more traditional legal systems (customary law).
When the systems developed, the idea was that certain issues (such as commercial transactions) would be covered by colonial law, and other issues (family and marriage) would be covered by traditional law. Over time, those distinctions tended to break down, and individuals would choose to bring their legal claims under the system that they thought would offer them the best advantage.
Legal pluralism also occurs when different laws govern different groups within a country. For example, in India and Tanzania, there are special Islamic courts that address concerns in Muslim communities by following Islamic law principles. Secular courts deal with the issues of other communities.
Since modern Western legal systems can also be pluralistic, it is misleading to discuss legal pluralism only in relation to non-Western legal systems. Legal pluralism may even be found in settings that might initially appear legally homogenous. For example, there are dual ideologies of law within courthouses in the US, as the formal ideology of law as it is written exists alongside the informal ideology of law as it is used. The discussion on the internal and external plurality of legal systems is called sociology of law.
Sources of Islamic law include the Koran, Sunnah and Ijma, but most modern Western nation states take the basis of their legal system from the Christian superpowers of old (Britain, France etc.). That is also why moral laws found in the Bible have actually been made full-fledged laws, with the initial grundnorm set far back in legal history, hence fulfilling the priority of both the positivists and the naturalists.
Legal pluralism also exists to an extent in societies where the legal systems of the indigenous population have been given some recognition. In Australia, for example, the Mabo decision gave recognition to native title and thus elements of traditional Aboriginal law. Elements of traditional aboriginal criminal law have also been recognised, especially in sentencing. That has, in effect, set up two parallel sentencing systems. Another example is the Philippines whose customary ways of indigenous peoples in the Cordilleras are recognized by the Philippine government and in Kalinga, Bodong is the means used by the people to settle disputes: since it had been very effective for them, it is still widely practiced.
There is some concern that traditional legal systems and Muslim legal systems fail to promote women's rights. As a consequence, members of the Committee on the Elimination of Discrimination against Women (CEDAW) have called for a unification of legal systems within countries.