Arms control agreements remain essential to global security, but their outcomes hinge on more than tactics at the table or technical substance. This chapter examines the “third dimension” of negotiation—the structural and contextual forces that shape bargaining environments—and highlights two understudied factors: power asymmetry and the role of narratives as costly signals. By drawing on historical cases, theoretical debates, and the evolution of modern treaty regimes, it shows how disparities in power and the credibility of strategic narratives decisively influence agreements. The analysis underscores the need for deeper quantitative and qualitative study of these dynamics, especially as a rapidly changing international system tests the implementation, enforcement, and credibility of the global arms control regime. Arms control and disarmament agreements are vital to global, regional, and state security and peace. These tools help the international community manage and mitigate the risks associated with the proliferation, stockpiling, and deployment of weapons. Beyond limiting the quantity of weapons, these agreements also serve as mechanisms for building trust, preventing escalation, and fostering long-term cooperation among nations with competing security interests.