One of the central mandates of the 1964 Wilderness Act is that "each agency administering any area designated as wilderness shall be responsible for preserving the wilderness character of the area." Although wilderness comprises about 20 percent of National Forest System lands (over 35 million acres), the agency lacks a way to evaluate progress in fulfilling this mandate. This document, developed by the Forest Service Wilderness Monitoring Committee, lays the conceptual foundation for a national assessment of how wilderness character is changing over time.