Let's begin with the cooperative aspects of the relationship. There are numerous areas in which the Unites States and China acknowledge shared interests, and acknowledge the benefit of cooperation. The threat of terrorism, the instability on the Korean peninsula, the desire for a stable and prosperous international economy, and a growing concern with climate change, are major examples. But cooperation in pursuit of these objectives frequently seems to fall short of the ideal. In fact, mutual dissatisfaction with each other's performance, in advancing supposedly common interests, is a regular theme in the US China relationship. One of the clearest examples of this problem involves North Korea. China and the US both say, that they seek the denuclearization of the Korean Peninsula, and oppose North Korea's development and deployment of ballistic wi, missiles and nuclear weapons. But the US accuses China of not using all possible leverage in pursuit of those objectives, of not imposing tough enough sanctions against Pyongyang, or not being sufficiently and openly critical of North Korea's transgressions. China, on the other hand, insists that its seeming reluctance is justified. It argues that economic sanctions are unlikely to be effective, unless they are so severe as to threaten the collapse of the North Korean economy. And in that case, Beijing points out, China would face much higher costs and risks, than with the United States. A collapsing North Korean economy would generate large flows of refugees from Korea into northeast China, a part of the country that does not have the capacity to absorb and accommodate them. It would also raise the question of the future of North Korea's nuclear weapons arsenal. So why can cooperations who advance common interests produce dissatisfaction and indeed argument, rather than strengthen a relationship? One problem particularly evident in the case of Korea, is that Chinese and American interests on key international issues, while overlapping and complementary, are not identical. [COUGH]. In particular, with regard to Korea, China and the United States define the seemingly common goal maintain stability on the peninsula very differently. To the US stability means preventing the outbreak of another Korean war, and preventing North Korea from deploying or exporting weapons of mass destruction. To China those goals are not unimportant, but they are less important than preventing the collapse of the North Korean regime, and that goal is far more important to Beijing than to Washington. In other words both countries use the same term stability to define their interest, their interests therefore, appear to be common. But if we look more carefully at what they mean by stability, we see that they mean different things for different reasons, and that obviously complicates their cooperation. Well not so evident in the Korean situation. There are other factors that, past and present, have obstructed cooperation between China and the United States. One is the cost involved, cooperation involves a variety of costs for both parties that they would prefer not to pay or at least to minimize. Sometimes a country is not eager to be seen as cooperating with another, because of its differences on other issues, or because cooperation might complicate its relations with third parties. When American and Chinese leaders started talking about building what they then called a constructive strategic partnership in the 1990s, strong objections were raised by Japan, which feared that a closer US-China relationship, especially if it used the word strategic, would come at the expense of its military alliance with the United States. Another cause stems from the fact that cooperation requires the dedication of resources to achieve a common objective, that not only raises the question of the distribution of costs and benefits among the collaborating parties, but can also require a degree of transparency about resources and leverage that one or both countries may prefer not to give. Yet another potential cost is the lost, the loss of autonomy and the acknowledgment of dependence, that an agreement to cooperate can entail and imply. Even at the height of the US-China United Front, as it was called, against the Soviet Union in the 1970's, this attitude was evident on the Chinese side. As Henry Kissinger has summarized the Chinese approach, Chinese leaders consistently denied that it needed or even wanted protection against Moscow, even they sought cooperation against Soviet expansion in Asia. According to Kissinger, Mao described the two countries as acting hand in hand in dealing with Moscow. But his comments strongly implied that in reality the two countries coordination, would be conducted more at arms length. Now consider it a concern with all of these different cost is understandable. But in the case of the US-China relationship, China's seeming reluctance to cooperate fully with the United States, has given it the reputation of being, if not a free rider, at least what one colleague of mine has recently called a cheap rider, trying to get the benefits of cooperation at the lowest possible cost. That perception can give rise to a level of mistrust, that can not only reduce the prospects for cooperation on the particular issue in question, but can spread to and in some sense poison other aspects of the relationship as well. So while China and the US are likely to continue to cooperate in coming decades, much will depend on whether that cooperation is open and enthusiastic, or hidden and grudging. And on whether each side is satisfied with regard to the costs and benefits of that cooperation whether they are shared equitably.