由於小布希政府時期政策上的相對忽視，使得美國在亞太地區多軌、多層次的區域主義發展進程中，未能取得霸權領導地位，錯失主導形塑區域架構之先機。2009年歐巴馬政府上任後，多次宣示「重返亞洲」企圖，繼而啟動多項亞太政策，並著墨於區域多邊途徑，近兩年來所推動政策逐步落實，美國對亞太區域主義發展之影響亦隨而增加。本文探討在美國「重返亞洲」之戰略轉移背景下，所採行之區域多邊途徑對未來亞太區域主義發展之意涵。文中舉三個美國具體參與之途徑與內涵：東協區域論壇、東協國防部長擴大會議、及東亞高峰會，其中參與東亞高峰會對區域主義發展之影響較其他兩者大，對東亞共同體建構、東亞高峰會議題設定、及所謂的「東協中心性」注入新變數，可能激化強權角色，使新現實主義中的結構因素超過新自由制度主義的建制規範，主導未來亞太區域主義的發展。

Due to policy negligence in the Bush administration, the United States failed to play a leading role in the multi-track and multi-layered process of Asia-Pacific regional institution-building. After Obama took over the Presidential office in 2009, new policies were adopted to redirect the U.S. strategic pivot to Asia. The regional multilateral approach in particular has boosted the U.S. leverage over regional developments in the past two years. This paper discusses the implications of U.S. multilateral approach to the development of Asia Pacific regionalism against the strategic backdrop of U.S. return to Asia. The U.S. participation in East Asia Summit, as opposed to ASEAN Regional Forum and ASEAN Defense Ministerial Meeting Plus, is expected to have a greater impact on regional dynamics in three aspects: the dynamics of East Asia community building, the agenda setting in East Asia Summit, and the efficacy of ASEAN centrality. The new developments may lead to another round of geo-strategic competition among powers. Structural factors addressed in neo-realism might surpass the effect of regime building suggested in neoliberal institutionalism to explain the future of Asia-Pacific regionalism.