Security cooperation in East Asia lags behind other forms of regional coopera- tion. The relationship among China, Japan, and the United States—the most powerful security actors in the region—exemplifies this broad pattern of exten- sive economic interaction with limited security cooperation to date. The chapter focuses on three questions in particular: (1) What and where is the demand for security cooperation in tomorrow’s East Asia? (2) What role can China-Japan- U.S. trilateral cooperation play? and (3) What should be the role of other regional actors, including South Korea?