The Taiwan question remains one of the most sensitive and intractable issues in China-U.S. relations. The Communist Party of China (PRC) regards Taiwan’s reunification as both a historical mission and a prerequisite for the great rejuvenation of the Chinese nation, and it has not renounced the use of force to achieve this objective. By contrast, the United States seeks to preserve the cross-Strait status quo through a policy of strategic ambiguity, calibrating deterrence against both forcible unification and formal independence from either side of the Strait. Despite these fundamentally divergent long-term objectives, Beijing and Washington have at times shared immediate interests in deterring moves toward Taiwanese independence and preserving stability, as seen during the 1995–96 Taiwan Strait Crisis. Periods of strategic cooperation have occasionally prompted Washington to show greater sensitivity to Beijing’s core concerns on Taiwan. This chapter contends that the shifting balance between strategic competition and cooperation in China–U.S. relations constitutes a critical external determinant of the policy space available to Taipei. Within the triangular structure linking the two sides of the Strait and the United States, Beijing and Washington function simultaneously as constraints and enablers, shaping—and at times delimiting—the trajectory of Taiwan’s mainland policy.