This chapter introduces the paradox at the heart of Taiwan’s mainland policy: it has been remarkably stable in its broad commitment to the status quo while also prone to sudden volatility driven by electoral turnover and external crises. Using the example of the Taiwanese leader Lai Ching-te’s 2025 controversial remarks and the People’s Republic of China (PRC)‘s sharp response, the chapter situates the Taiwan issue as both an enduring domestic fault line and a central flashpoint in China–U.S. rivalry. It reviews existing literature on external constraints (Beijing’s pressure and Washington’s balancing), domestic drivers (party politics, leadership, institutions, and identity), and economic interdependence across the Taiwan Strait, while highlighting shortage in integrative explanations. To address these, the chapter outlines the book’s analytical approach, introducing the two-level punctuated-equilibrium theory that links internal partisan competition with external triangular pressures. Methodologically, it combines documentary analysis, comparative history, and public opinion surveys. This chapter thus sets the stage for a systematic exploration of Taiwan’s cross-Strait policy change.