US-Russia ballistic missile defense (BMD) cooperation can improve strategic stability between both countries, but this cooperation would pose a potential threat to China’s strategic security, especially if it is a closed and deep cooperation. The United States and Russia should make their bilateral cooperation an open regime, and let China and other countries join, so that improvement of US-Russia strategic stability is not based on the sacrifice of strategic stability with China and other countries. China and the United States may also cooperate on BMD in areas of early warning and mutual launch notification. The security costs of these cooperative measures are very low, and the benefits would improve stability, confidence, and mutual trust. Finally, BMD cooperation between the United States and its East Asian allies (Japan and Taiwan) is threatening Sino-US strategic stability. The United States could improve Chinese confidence by increasing transparency about and limiting the performance of BMD systems.