In the past 150 years, educational systems have expanded and become integrally linked with economic, political, and social status in modern nation-states. As the stakes for education have risen, so has the call for more and improved use of scientific evidence as a basis for educational policymaking. Evidence from averaged scores on international assessments of math and science achievement in particular have become important indicators of national political and economic strength, but there are many different kinds of evidence to consider. For example, high-stakes consequences resulting from averaged academic achievement scores exist for students and schools in the United States but even more so in other countries, such as Japan. However, how and why evidence is used for educational policymaking both in the United States and around the world are the larger questions this chapter addresses. To investigate the uses of evidence for educational policymaking, this chapter asks two fundamental orienting questions: Why use evidence in educational policymaking? And why is evidence-based educational policymaking a global phenomenon? The answer to the first orienting question serves as a foundation for introducing relevant macrotheoretical perspectives and exploring the motivations and agendas that drive educational policy and decision making. The answer to the second orienting question provides a snapshot of the scope of the evidence-based decision-making phenomenon and some reasons why it has gained significance among educational policymakers around the world.