In Islamic jurisprudence, qiyās (Arabic قياس) is the process of deductive analogy in which the teachings of the Hadith are compared and contrasted with those of the Qur'an, in order to apply a known injunction (nass) to a new circumstance and create a new injunction. Here the ruling of the Sunnah and the Qur'an may be used as a means to solve or provide a response to a new problem that may arise. This, however, is only the case providing that the set precedent or paradigm and the new problem that has come about will share operative causes (illah). The illah is the specific set of circumstances that trigger a certain law into action.

Both Sunni Islam and Shia Islam share Qur'anic interpretation (tafsīṛ), the pattern of Muhammad (sunnah), and scholarly consensus ijma as sources of Islamic law, although the two differ significantly with regards to the manner in which they use these sources.

Individual opinion (ra’y) and deductive analogy (qiyāṣ) play an important role in many Sunni legal traditions, forming the basis of much of Sunni jurisprudence. In addition to tafsīr, the sunnah, and ijmā’, Sunni traditions generally regard qiyas as the fourth source of deducing the law. Other methods of deriving legal judgments such as mafhm al-nass (the clear implication of the text), tamthil (similarity or likeness), istihsan (juristic preference), or istislah (consideration of public interest), either explicitly rely on qiyas or use methods of analysis that are similar in their understanding of qiyas. However among Sunni traditions, there is a range of attitudes regarding the validity of these methods. Ahmad bin Hanbal and Dawud al-Zahiri for example, rejected qiyāṣ outright, arguing that to rely on personal opinion in law-making would mean that each individual would ultimately form their own subjective conclusions.