Every U.S. state and the District of Columbia maintain a system to collect and store education data. These systems vary widely in their scope and sophistication -- and, by extension, in their ability to provide information that can guide decision-making. Most states have developed statewide longitudinal data systems, which establish formal connections among systems from two or more of the following four core state agencies: early learning, K-12, postsecondary and workforce. Such systems make it possible to follow students' progress from early childhood to career. This Policy Guide goes beyond looking at the foundations and structures of statewide longitudinal data systems to explore how state leaders can more intentionally and effectively develop a culture that uses data to inform critical education decisions.