This chapter lays the theoretical groundwork for the argument. In the first section, I outline the legal regime governing armed conflict. The second section provides an initial definition of reciprocity and reviews two literatures explaining its importance to compliance with international legal regimes such as IHL. In section three, I outline what I am calling the “humanization of humanitarian law” thesis. This is the view that states are and can be expected to implement IHL obligations even if their adversaries do not. In section four, I present a more nuanced view of reciprocity. I demonstrate, via H. L. A. Hart’s theory of law as the union of primary and secondary rules, how states have maintained reciprocal strategies for dealing with IHL non-compliance through secondary rules. I then explain how the domestic, multi-actor setting of state decision making allows policy makers to use these secondary rules to respond to IHL non-compliance. In the last section, I examine logic of appropriateness theories found in the international relations and international law literatures that could serve as a basis for the humanization of humanitarian law thesis.