The recent sinking of the ROK Corvette Cheonan, China’s continuing growth, Japan’s volatile politics, and the US campaigns for denuclearization and nonproliferation are key factors in the effort to forge a regional security architecture in Northeast Asia. To better understand the challenges and opportunities and to explore the potential of the quadrilateral relationship among the United States, China, Japan, and the Republic of Korea, the Pacific Forum, the Research Institute for Peace, and the Security Center for International and Strategic Studies, Peking University held the latest in an ongoing trilateral dialogue, and welcomed full participation by a delegation from the Republic of Korea, which joined the dialogue as observers in 2009.