China's remarkable gains in science over the past 25 years have been well documented (e.g., Jin and Rousseau, 2005a; Zhou and Leydesdorff, 2006; Shelton & Foland, 2009) but it is less well known that China and the United States have become each other's top collaborating country. Science and technology has been a primary vehicle for growing the bilateral relationship between China and the United States since the opening of relations between the two countries in the late 1970s. During the 2000s, the scientific relationship between China and the United States--as measured in coauthored papers--showed significant growth. Chinese scientists claim first authorship much more frequently than U.S. counterparts by the end of the decade. The sustained rate of increase of collaboration with one other country is unprecedented on the U.S. side. Even growth in relations with eastern European nations does not match the growth in the relationship between China and the United States. Both countries can benefit from the relationship, but for the U.S., greater benefit would come from a more targeted strategy.