Since the 2011 uprising in Egypt, the Egyptian state has increasingly put to use the charge of defamation of religion (izdira’ al-din) to regulate speech acts and practices under the pretense of protecting religion, principally Islam. The charge, though sometimes thought to be a “medieval” hangover signaling Egypt’s incomplete or failed project of secularism, is based on a law that was added to Egypt’s penal code in 1982. It is part of a distinctly modern genealogy of the politics of religious freedom. Focused on that genealogy, this paper examines how religious freedom—a concept that emerged out of the experience of sectarian conflict and the rise of the modern state in Western Europe—was translated and accumulated meaning in the increasingly bounded political space of Egypt under colonial and semicolonial rule. Historians have observed that missionaries—both foreign and local—in Egypt understood religious freedom as the right to proselytize and the right of (Muslim) Egyptians to convert, since Egyptian law did not protect conversion out of Islam. For many Egyptians, by contrast, religious freedom meant the right to protect one’s religion from what was perceived as an outside assault. This paper follows the contingent formation of this conceptual paradox in the legal and political discourse of early twentieth-century Egypt and traces religious freedom’s manifestations through the 1930s. I show how the fluidity and instability of this concept, central to traditions of political liberalism, elicited continuous debates over its meaning. In Egypt’s interwar political context, and particularly in the face of a perceived missionary assault justified through the discourse of religious freedom, Egyptians articulated notions of this concept centered around feelings of moral injury and offense and through a local vernacular of ethics that, while embedded within the Islamic tradition, was shared across religious divides. In tandem, the Egyptian state gradually encoded these sensibilities into expanding positivist civil law as part of establishing and maintaining public order, thus delimiting Egypt’s political and, perhaps ironically, religious imaginaries. The paper should appeal to scholars of ethics, law, liberalism, religion, secularism, and modern Egyptian and Middle Eastern history.