The China-U.S. Science and Technology Cooperation Agreement, which has been renewed every five years since the two countries signed it in 1979, will expire again this year. But it is uncertain whether the agreement will be renewed again amid the U.S. antagonism toward China. What have the two countries gained from 45 years of science cooperation? Why is there opposition now? How can China and the U.S. strike the right balance between openness in science and safeguarding national security?