In our most recent game, The Last of Us, the sound team at Naughty Dog created a powerful dialog system that allows enemy and ally NPCs to converse with each other and the player character in realistic ways. This system takes into account rich contextual information, including individual knowledge, collective knowledge, global game state, and information about the surrounding environment. This system puts a great deal of power directly into the hands of the sound designers, freeing the programmers to focus on AI behaviors. This talk will explore the requirements and problems inherent in any NPC dialog system, and describe the baseline features required of any such system. The talk will then investigate the unique problems Naughty Dog faced in The Last of Us, and describe the systems developed to solve them. It will then conclude with Q&A and a discussion of some ideas for future work.