National park resource management planning requires ecological information describing the objectives to be achieved. This information must be quantitative and unambiguous. Since most acts creating United States national parks, beginning with the Yellowstone National Park Act of 1872, specify that these parks should be maintained in a natural condition, resource management objectives for each national park must be defined in terms of quantitative standards of naturalness. Such quantitative standards of naturalness do not yet exist for any national park in the United States. Although this article focuses on US national parks, the same problem exists in national parks, reserves, and wilderness areas throughout the world. The physical evidence needed to develop quantitative standards of naturalness is rapidly disappearing because of the effects of management fires, wildfires, decomposition, successional changes, and other disturbances. Therefore, a nationwide “rescue ecology” program is recommended to recover as much remaining ecological information as possible before it is lost. This information is essential for developing quantitative standards to restore naturalness to national parks.