What is the ruling on Shura (consultation) in Islam, and is it obligatory or recommended? If it is obligatory, upon whom is it obligatory?

Consultation (Shura) is a legitimate Islamic principle whose implementation is emphasized in matters that are ambiguous and for which there is no explicit text. The Shari'ah evidences from the Quran, the Sunnah, and the actions of the Prophet (peace be upon him) and his Companions, indicate its legitimacy and importance. Scholars have differed on whether it is obligatory or recommended for rulers, but for those other than rulers, it is recommended.