This chapter explains why two consensus-based Asian regional organizations have produced sharply different records in security governance. It argues that ASEAN scales security cooperation not through supranational authority, but through the steady accumulation of diplomatic infrastructure, dense meeting routines, and layered fora that translate sovereignty sensitivity into managed informality and practical coordination. By contrast, SAARC's institutional design embeds high veto points and a constitutive rule excluding bilateral and contentious issues, which, when paired with persistent strategic rivalry, narrows the space of possible diplomacy and prevents security initiatives from being routinized. Using founding charters, key treaties, and institutional practice, the chapter shows how regionalism functions as diplomacy, shaping agendas, producing norms, and structuring crisis response. The concluding section draws implications for Asian order in an era of Indo-Pacific contestation and hybrid threats.