This article examines the interaction of Coptic Christians with Islamic legal institutions in provincial Egypt on the basis of a corpus of 193 Arabic legal documents, as well as relevant Coptic ones, dating to the 2nd-5th/8th-11th centuries. I argue that around the 3rd/9th century Islamic Egypt’s Christian subjects began to make routine use of Islamic legal institutions to organize their economic affairs, including especially inheritance and related matters internal to Christian families. They did so in preference to the Christian authorities and Coptic deeds that had been their standard resource in the first two centuries of Muslim rule. The changing character of the Egyptian judiciary encouraged this shift in practice, as qāḍīs who adhered to fiqh procedural rules increasingly filled judicial roles formerly held by administrative officials. By eschewing and nudging into disuse a previously vital Coptic legal tradition, Christian provincials participated in the Islamization of ʿAbbāsid and Fāṭimid Egypt.