My dissertation examines the evolving discourse on blasphemy as an Islamic legal category among capital crimes in early and medieval Islamic history, from 630 AD until the fall of the Ottoman empire. Historians have generally understood blasphemy, known as sabb in the Islamic context, to connote any act constituting insult to the Prophet Muhammad or God. Acts of sabb are generally considered to be Hudud crimes in Islamic law. Hudud crimes were deemed to be mandated by God and hence unalterable by human beings, requiring mandatory sentences in the form of corporal or capital punishment. A common view among historians has been that Muslim jurists were unanimous in asserting that any individual, whether Muslim or non-Muslim, who insulted the Prophet was to be swiftly executed, and that not doing so would be considered a heinous violation of God's law.Historical sources however, present a more complex picture. A stringent response to blasphemy that leaves no room for mitigation developed late in Islamic thought—the 12th century rather than the 7th, in which Islam emerged. Even after sabb was criminalized, Muslim thinkers mounted principled and orthodox opposition to the execution of Muslims and non-Muslims for this crime. A comprehensive intellectual history on the development of blasphemy as a legal category has yet to be published, and it is this void that this dissertation seeks to fill in the academic literature. I examine sections of Islamic legal texts which deal with blasphemy chronologically, from the formation of the genre in the early centuries of Islam till its sophisticated formulation in Mamluk and Ottoman times and examine doctrinal shifts according to time period, geography, and legal school. Most of my sources exist only in manuscript form at the National Lib. of Jordan as well as at the Ctr for Documents & Manuscripts at the Univ. of Jordan, without which my project will be incomplete. I am applying for an SSRC-IDRF to procure these materials.