This volume constitutes the refereed proceedings of the 17th International Conference on Decision and Game Theory for Security, GameSec 2026, which took place in Ann Arbour, Michigan, USA, in October 2026.

The 29 full papers included in the proceedings were carefully reviewed and selected from 57 submissions. They were organized in topical sections as follows: Equilibrium Computation and Game-Theoretic Foundations; Information Design, Mechanism Design, and Strategic Incentives; Deception, Stackelberg Games, and Cyber-Physical Security; AI, LLM, and Agent Security; Learning-Based Security and Networked Systems.