Progress toward the successful completion of any program improves as the resources available to that program increase. International cooperation is a mechanism that can increase the resources available to the U.S. fusion program. Viewed historically as a science program, the progress in fusion R&D in the United States has been significantly enhanced through this mechanism. However, as fusion moves increasingly into engineering development toward commercial application, the benefits of science exchange may appear to be increasingly counterbalanced by (a) the potential increase in administrative costs and time delays and (b) the opportunity cost associated with sharing potentially proprietary technology information. The transition between fusion development phases (scientific to engineering) requires a reassessment and revamping of the scientific nonstrategy for international cooperation. The assessment of costs and benefits of previous mechanisms for international cooperation provides some fundamental conclusions that should be considered in the development of any new fusion strategy. The major conclusion is that international cooperation will be essential for meeting the U.S. commercial-development milestones, but that this mechanism must be used judiciously with effective U.S. program management. The major recommendations of the study are that the U.S. program should (a) actively pursue playing a significantly stronger leadership role in the international arena, (b) develop a stronger linkage with the Japanese program, and (c) pursue policy that does not require a strong dependency on other programs for the development of critical technology.