This chapter explores how the system of US bilateral alliances and informal strategic groupings in the Indo-Pacific affects crafting allied cyber deterrence strategies in region. Based in deterrence and alliance theory, this chapter surveys cyber threats faced by US allies and partners in the region and views of cyber deterrence to form a general framework of allied cyber deterrence strategy. It uses the US–South Korea alliance as a case study for allied cyber deterrence strategy, with a special focus on the impact that South Korea assuming wartime operational control of allied military forces could have on cyber deterrence on the Korean Peninsula. This chapter argues that, just as concepts of extended deterrence have had to evolve, the cyber domain will force the United States and its allies to reconceptualize peacetime and wartime operational control.