More states are thinking about their data systems and how to give decision-makers the information they need. As states work to create successful education and career pathways, they need transparent, well-structured and well-governed data systems. To learn more, our team conducted a 50-State Comparison on state longitudinal data systems to collect relevant policies and practices in use and understand where states are in the process of creating effective data systems. Informed by the data from the 50-State Comparison, this Policy Guide pulls together recent reports, tools and surveys from the field and demonstrates an emerging consensus about the key elements of an effective state longitudinal data system that responds to diverse audiences' needs. State policymakers can use this resource to assess their own data system against emerging best practices highlighted in this Policy Guide.