This essay synthesizes the most recent and rigorous research on student loan debt. It focuses on basic questions about who borrows, how much, and whether debt affects behaviors. Answers to these questions are necessary for informing federal student loan policymaking, yet the research findings are surprisingly mixed because of poor data quality, research design challenges, and the growing heterogeneity of borrowers. This ambiguity makes federal policymaking difficult when questions about the benefits and burdens of student loan debt are left unanswered. By synthesizing the current research, this essay helps answer some of these questions while calling attention to others.