In the 21st century, the United States will increasingly rely on cyberspace to advance its national interests within a strategic environment characterized by volatility, uncertainty, complexity, and ambiguity. Concurrently, our adversaries are afforded increased opportunities to undermine our efforts by conducting a broad spectrum of nefarious activities in the digital domain. While not all of their acts will pose a direct and imminent threat to the nation s security, some will. Given these challenges, cyber strategists, government leaders, and scholars frequently disagree over whether the U.S. should establish thresholds (or red lines) for using military power when responding to hostile acts in cyberspace against government computer networks. This paper argues that delineating indistinct vice ambiguous or distinct red lines for hostile acts in cyberspace will better protect U.S. government networks and provide policymakers and military leaders ample flexibility to tailor response options in the same manner they are developed for threats in the other global domains.