This book investigates the transformative potential of Big Data in advancing Evidence-Based Policymaking (EBPM). As governments grapple with complex challenges, there is increasing demand for using scientific evidence to enhance the quality of policymaking. Through an interdisciplinary approach integrating public administration, Social Big Data analysis, and economics, this book provides practical implications for governments to advance EBPM, while demonstrating how to leverage Social Big Data to support policymaking with concrete policy cases. This book first explains the fundamental concepts of EBPM, including what counts as evidence, why evidence matters, and what procedure ensures effective EBPM implementation. Part II reveals the current status of EBPM practices in two countries: the UK, as a leading nation in EBPM practices and Japan in the nascent stages of adoption. This part examines the persistent shortcomings, and systemic challenges faced by both governments in advancing EBPM. Furthermore, Part III presents empirical analyses across three policy domains: tourism promotion, human mobility control during the Covid-19 pandemic, and house price estimation. The analyses used Social Big Data sources, e.g., Google Trends, SNS, and Google Mobility, to quantify important policy factors and provide evidence for policymaking and evaluation. This book stands out for its contributions in two key areas. First, it reveals the current status of EBPM practices in the UK and Japan, thereby addressing a critical research gap in cross-national EBPM studies. Second, it contributes to both academic research and policy practice by proposing a data-driven EBPM approach and demonstrating its application through specific policy analysis cases.