How much visitor use can be accommodated in national parks without unacceptable impacts to park resources and the quality of the visitor experience? Visitor capacity is a long-standing and increasingly urgent issue in national parks. Several management frameworks have been developed to help define and manage visitor capacity, and all of these frameworks rely on formulation of indicators and standards of quality for park resources and the visitor experience. Application of these frameworks can be informed by a program of research, including stakeholder surveys, normative theory and methods, visual research methods, analysis of tradeoffs in outdoor recreation, and computer-based simulation modeling. These methods have been applied in a program of research on visitor capacity in the U.S. National Park System.