U.S. competitors pursuing meaningful revision or rejection of the current U.S.-led status quo are employing a host of hybrid methods to advance and secure interests that are in many cases contrary to those of the United States. These challengers employ unique combinations of influence, intimidation, coercion, and aggression to incrementally crowd out effective resistance, establish local or regional advantages, and manipulate risk perceptions in their favor. So far, the United States has not come up with a coherent countervailing approach. It is in this gray zonethe awkward and uncomfortable space between traditional conceptions of war and peacewhere the United States and its defense enterprise face systemic challenges to U.S. position and authority. As a result, gray zone competition and conflict should be pacers for defense strategy. For defense and military strategists, the gray zone is a broad carrier concept for a universe of often-dissimilar strategic challenges. Defense-relevant gray zone threats lie between classic war and peace, legitimate and illegitimate motives and methods, universal and conditional norms, order and anarchy; and traditional, irregular, or unconventional means. All gray zone challenges are distinct or unique, yet nonetheless share three common characteristics: hybridity, menace to defense/military convention, and risk-confusion. First, all gray zone challenges are some hybrid combination of adverse methods and strategic effects. Second, they menace American defense and military convention because they simply do not conform neatly to a linear spectrum of conflict or equally linear military campaign models. Finally, they are profoundly risk-confused; as such, they disrupt strategic risk calculations by presenting a paralyzing choice between action and inaction. The hazards associated with either choice appear to be equally high and unpalatable.