Since the turn of the century, China has adopted a wide range of approaches to address maritime territorial and boundary disputes, defying simple categorization. Despite its rapidly growing power, Beijing has not invariably utilized an assertive, escalatory posture, nor has it consistently taken an accommodating, de-escalatory stance as its "good neighborly diplomacy" would suggest. When China has chosen to escalate, its strategies have varied widely in both nature--nonmilitary or military--and intensity. What accounts for these variations? And, what do these variations mean for the potential of maritime conflict and cooperation in Asia?In Simmering Seas, Shuxian Luo presents the first systematic examination of China's escalation and de-escalation decisions and strategies in the East China Sea, South China Sea, and the Yellow Sea from 2000 to 2022. Drawing on granular data, untapped authoritative Chinese sources, and over 150 interviews with officials and experts across the Asia-Pacific and the United States, Luo reveals that China is neither a reckless aggressor nor a peaceful giant. Instead, it is a calculating player, often trapped by its own domestic politics and restrained by its international aspirations. Luo explains that China tends to opt for escalation when the potential domestic political cost of moderation outweighs the anticipated international cost of assertiveness. Furthermore, China is most likely to engage in military escalation when it seeks to compel a rival claimant to retract undesired actions.Original and authoritative, Simmering Seas explains the history and strategic calculations behind the headlines covering disputes in maritime Asia.