FATWA

A fatwa is an Islamic religious ruling, a scholarly opinion on a matter of Islamic law.

A fatwa is issued by a recognized religious authority in Islam. But since there is no hierarchical priesthood or anything of the sort in Islam, a fatwa is not necessarily "binding" on the faithful. The people who pronounce these rulings are supposed to be knowledgable, and base their rulings in knowledge and wisdom. They need to supply the evidence from Islamic sources for their opinions, and it is not uncommon for scholars to come to different conclusions regarding the same issue. (Answers.com)

In the early days of Islam, fatawa were pronounced by distinguished scholars to provide guidance to other scholars, judges and citizens on how subtle points of Islamic law should be understood, interpreted or applied. There were strict rules on who is eligible to issue a valid fatwa and who could not, as well as on the conditions the fatwa must satisfy to be valid.

According to the Usul al-fiqh (Principles of Jurisprudence), the fatwa must meet the following conditions in order to be valid:

The fatwa is in line with relevant legal proofs, deduced from Qur'anic verses and hadiths; provided the ahadith was not later abrogated by Prophet Mohammed.
It is issued by a person (or a board) having due knowledge and sincerity of heart;
It is free from individual opportunism, and not depending on political servitude;
It is adequate with the needs of the contemporary world.

Today, with the existence of modern independent States, each with its own legislative system, and/or its own body of ulemas, each country develops and applies its own rules, based on its own interpretation of religious prescriptions. (Wikipedia)