This chapter sets the stage for the book by explaining why EBPM matters and how the rapid expansion of Big Data is reshaping the possibilities and challenges of using evidence in government. Around the world, governments face mounting pressure to justify policies with credible evidence while responding to increasingly complex social and economic problems. At the same time, digital technologies are generating vast amounts of data on human behavior, mobility, and preferences. This book asks how these new data sources can be used in a responsible and meaningful way to strengthen EBPM in practice, rather than simply adding more information to an already crowded policy environment. The chapter proceeds by first outlining the research background and the policy debates that motivate the study. It then clarifies the purpose of the book and formulates the main research questions that guide the subsequent empirical analyses. The research design and data sources are briefly introduced, with particular attention to how Big Data are combined with conventional statistics. The chapter also defines the scope of the study in terms of policy areas, the type of data, and explains what is not covered. Finally, it provides an outline of the book’s structure and explains how the different parts and chapters work together to answer the research questions and to rethink EBPM in the Big Data era.