This article explores the formation and evolution of regional institutions in the Asia-Pacific and East Asia. Employing a historical institutionalist framework, this article argues that both Asia-Pacific and East Asian regional institutions were created at critical junctures, precipitated by extra-regional developments that called the legitimacy of existing institutional mechanisms into serious question. Preexisting institutions greatly shaped the institutional design of the subsequent regional institutions, revealing a path-dependent nature of institutional evolution. The timing and sequence of regional institution building is an important factor for explaining institutional change. …