The Martens Clause was a last-minute compromise that saved the 1899 Hague Convention with Respect to the Laws and Customs of War on Land. In its original formulation, the clause shielded individuals under “the protection and empire” of international law, principles of humanity, and the dictates of the public conscience. F. F. Martens, its author, was Russia’s greatest international law scholar and occasional diplomat. He saw no application for his work in the nineteenth-century internal affairs of his sovereign, notwithstanding the transnational terrorism that plagued (and ultimately destroyed) the Russian Empire. As the relationship between individual rights and state sovereignty dramatically changed in the twentieth century, the reach and importance of the Martens Clause grew. Its value continues to this day. Its history helps refute the claim that international humanitarian law is ill-suited for twenty-first century transnational terrorism. But the Clause is not, and never was, a panacea.