Many states are passing "free" college plans, and policymakers at both the state and federal level continue to debate the merits of national "free college" or "debt-free college" proposals, also known as Promise programs. Both federal and state "free" college proposals are geared toward a policy objective of not just reducing costs for students already intent on pursuing higher education, but also changing behavior to increase access and entry into higher education. Specifically, an important goal of financial aid such as Promise programs is to increase overall student demand to attend college--particularly amongst low-income students who would otherwise be deterred due to the real or perceived high cost of attending college. This report summarizes the literature on the impact of financial aid and price on college student enrollment, surveying research on "free" college programs, financial aid programs, and tuition rate changes. The review shows potentially significant effects from programs, but illuminates how difficult projecting those effects can be. The authors also review the ways in which states and public colleges budget for new enrollees. In addition, the authors propose a policy framework for using existing research to adequately fund institution capacity needs that may result from new large-scale affordability programs.