Ijmā' (إجماع) is an Arabic term referring ideally to the consensus of the ummah (the community of Muslims, or followers of Islam).

The hadith of Muhammad which states that "My community will never agree upon an error" is often cited as support for the validity of ijmā'. Sunni Muslims regard ijmā' as the third fundamental source of Sharia law, after the divine revelation of the Qur'an, the prophetic practice or Sunnah. The analogical reasoning or qiyas is described as fourth source in Sunni Islam, whereas Shi'a Islam uses 'aql (intellect). Many conservative Muslim writers have claimed that the use of ijmā' makes Islamic law compatible with democracy. Usuli Shia accepts ijmā' under restricted conditions as a source of Islamic law. Technically it is “the unanimous doctrine and opinion of the recognized religious authorities at any given time”.

Various proponents of liberal movements within Islam criticize the traditional view that ijmā' is only a consensus among traditional Islamic scholars (Arabic ulema). They claim that truly democratic consensus should involve the entire community rather than a small and conservative clerical class, especially since there is no hierarchical system in Islam.