This article describes how Islamic and Frankish legal devices complemented each other and were even combined to settle disagreements in the late medieval Middle East. For this purpose, it focuses on two legal institutions that provided responses to the biases of Islamic law against non-Muslims and to the prejudices of Franks against the local law. The first are the notaries sent to the Mamluk cities by the Venetian government to draw up legal documents and to support the transactions of Venetian merchants. The second are the new royal or siyāsa courts implemented by the sultans, where justice was dispensed by government officials instead of by traditional judges, or qāḍīs. Specifically, the article discusses, in a comparative manner, what constituted proof for Christians and Muslims, whether minorities could bear testimony or not, and how notaries and judges dealt with unbelievers. A common notarial culture, together with the expansion of siyāsa jurisdiction over the affairs of foreigners, brought about a much deeper legal interplay than has previously been understood. Ultimately, it is argued that Mediterranean medieval societies had evolving attitudes toward justice and diversity, and approached their own legal traditions in ways compatible with the conflict resolution, while constantly borrowing legal concepts about difference from each other.