This report discusses the effects of the possible entry of Japan to the Trans-Pacific Partnership (TPP) negotiations. The TPP issue presents both risks and opportunities for the United States and Japan. On the one hand, it could reinvigorate an economic relationship that has remained steady but stagnant, by forcing the two countries to address long-standing, difficult issues, and allowing them to raise their relationship to a higher level. On the other hand, failure to do so could indicate that the underlying problems are too fundamental to overcome and could set back the relationship.