Theater strategy and theater security cooperation are two of the most important tools available in attaining national security. They offer an effective means for geographic Combatant Commanders to engage other countries, deter aggression, or resolve crises. However, there is little current, concise, and comprehensive guidance on how they are planned and implemented. This paper explains what theater strategy is, its basis, how it is formulated, and how it is executed with emphasis on theater security cooperation. The author illustrates the role in national affairs of theater strategy and security cooperation through examples from a case study leading up to and during Operation ENDURING FREEDOM in Afghanistan.