This chapter emphasizes the necessity of integrating scientific knowledge, socio-economic realities, and policy constraints, highlighting the significance of policy design in complex and uncertain environments. Considering East Asia’s rapidly growing economies, high energy demand, and energy systems heavily dependent on imports, the chapter outlines region-specific challenges and prospects. Using the uncertainties inherent in climate change and decarbonization as a starting point, it proposes an interdisciplinary framework—Policy Engineering—as an approach to decarbonization. While the IPCC Sixth Assessment Report (AR6) concludes that it is “unequivocal” that human activities are the main driver of climate change, scientific challenges remain, including model limitations, natural variability, and uncertainties in emission pathways. Historical climate studies also indicate the long-term influence of natural variability. Such scientific uncertainties affect policymaking, making the choice of base years and the reliability of projections crucial for building public trust. Climate uncertainties can be categorized into scientific, technological, economic, and social dimensions. Uncertainties related to the commercialization of new technologies, fluctuations in energy markets, and societal acceptance interact and constrain policy decisions. This chapter demonstrates the effectiveness of Policy Engineering methods that account for these multi-layered uncertainties. Tools such as scenario analysis, robust policy design, and real-options analysis are positioned to balance practical policy design with social acceptability. Policy Engineering is framed as an interdisciplinary approach that links scientific and technological knowledge with social and institutional mechanisms. Subsequent chapters aim to apply this framework to concrete policy issues and technological strategies, providing practical insights for building a sustainable and cooperative decarbonized society.