As global nuclear threats escalate, reassessing the effectiveness of nuclear deterrence strategies—particularly the U.S. nuclear extended deterrence (NED) posture—has become increasingly essential. This chapter introduces the concept of “institutional deterrence” or “institutional nuclear deterrence” as a framework for such an evaluation. Drawing on institutionalism from social science, the chapter identifies key institutions underpinning U.S. NED, focusing on mechanisms such as nuclear sharing, exemplified by the Nuclear Planning Group (NPG) within NATO. As a case study, the chapter examines the institutions supporting the United States–South Korea alliance and U.S. NED for South Korea, using the identified key institutional elements. Based on this analysis, it recommends that the United States and South Korea elevate their current nuclear consultative framework into NPG-Pacific, inclusive of other U.S. allies like Japan and Australia. It further suggests bolstering the forward deployment of U.S. nuclear assets near South Korea, adopting nuclear-sharing arrangements in the Pacific, and enhancing assurance statements with a focus on deterrence. Most importantly, the chapter advocates for further scholarly inquiry into the concept of institutional deterrence.