Educators and policymakers have become increasingly concerned about the issue of student absenteeism in general and, in particular, chronic absenteeism. This is because chronic absenteeism can have lasting effects on students' economic and social development. Children who are chronically absent have lower levels of school readiness upon entering kindergarten, are less likely to read at grade level by the third grade, show lower levels of social engagement, are more likely to drop of school, and are less likely to graduate from high school or attend college. All of these negative outcomes limit the long-term success of students in school and into adulthood. Specifically, dropping out of high school not only limits a person's long-term earning potential and career advancement, but can also significantly reduce potential tax revenues. From a systems perspective, chronic absenteeism disrupts the effective delivery of instruction, widens the achievement gap, and reduces state funding to schools. Although absenteeism is an old problem, there is now a new impetus for addressing it. The newly enacted Every Student Succeeds Act (ESSA) law requires the reporting of chronic absenteeism at school and district levels, and it allows the use of federal funds for preventive measures and training to reduce chronic absence. In addition, chronic absenteeism can be included as a school-quality indicator in state-level ESSA accountability systems. States will now have to establish data systems for tracking student absenteeism and report the information collected. This Research Brief goes beyond previous National Education Association (NEA) work by identifying and highlighting best practices aimed at reducing the problem of chronic absenteeism. [This brief was written in collaboration with the Center for Great Public Schools.]