The distinctive characteristics of Shi'ah Muslim Fiqh come from its sources, especially its interpretation of the Sunnah of the Prophet (s.a). The Ahadith of the Imams (a.s) are considerably important source of Shi'ah Muslim Fiqh. The Shi'ah accept the holy book, al-Quran, Sunnah, consensus (ijma'), in a particular sense, and reason (al-'aql) as basic sources of law. Other forms of reasoning such as Qiyas, Istihsan, and al-Masalih al-Mursalah are not considered Hujjah, legally authoritative.

However, differences of views according to Shi'ah Muslim scholars of Fiqh are difficult to avoid because of the difference in every one's perception of facts. The Shi'ah Muslim Fiqh enjoyed a particular order and consistency of discipline in the matters of Fiqh.

In Shi'ah Muslim principles it is not necessary to exercise Ijtihad 34 find the rules of Shari'ah from the original sources during the time of the Imams (a.s) yet the Shi'ah Muslim scholars of Fiqh did exercise Ijtihad in that period because of strong exhortations of the Imams (a.s). They would even apply certain principles of jurisprudence (usul) in deriving certain rules of Shari'ah 35.