This book examines China's participation in the United Nations (UN). There are two research components. First, the author seeks to find a pattern of China's multilateral diplomatic behavior in the UN by examining China's behavior toward peacekeeping operations and arms control issues during different leadership periods under Mao Zedong, Deng Xiaoping, and Jiang Zemin respectively. Second, a model is proposed to explain this pattern of behavior. By marrying rationalism and constructivism, this model argues that the amelioration of China's external security environment changes in its projected self-image. Furthermore, China's consistently strong view of sovereignty determines its evolving pattern of behavior in the UN.