This chapter addresses the challenges associated with assessing and improving the resilience of interdependent critical infrastructure systems under potential disruptive events. A specific set of analytical tools are introduced based on quantitative models of infrastructure systems operation and their functional interdependencies. Specifically, the game-theoretic attacker-defender and defender-attacker defender modeling techniques are applied to assessing the resilience of interdependent CI systems under worst-case disruptions, and advising policymakers on making pre-disruption decisions for improving the resilience of interdependent infrastructures. A case of interdependent power and gas systems is presented to show the proposed model and highlight the significance of protecting interdependent CIs.