As CCW states parties assess fully autonomous weapons and the way forward, the Martens Clause should be a central element of the discussions. The clause, which is a common feature of international humanitarian law and disarmament treaties, declares that in the absence of an international agreement, established custom, the principles of humanity, and the dictates of public conscience should provide protection for civilians and combatants. The clause applies to fully autonomous weapons because they are not specifically addressed by international law. Experts differ on the precise legal significance of the Martens Clause, that is, whether it reiterates customary law, amounts to an independent source of law, or serves as an interpretive tool. At a minimum, however, the Martens Clause provides key factors for states to consider as they evaluate emerging weapons technology, including fully autonomous weapons. It creates a moral standard against which to judge these weapons.