Congress has since added approximately 100 million more acres to the Wilderness System (see Table 1 ) among some 608.9 million acres of land managed by the federal land management agencies—the Forest Service in the Department of Agriculture, and the National Park Service (NPS), Fish and Wildlife Service (FWS), and Bureau of Land Management (BLM) in the Department of the Interior. In response, Congress enacted the Wilderness Act in 1964. The act reserves to Congress the authority to designate areas as part of the National Wilderness Preservation System. The Wilderness Act directed the Secretary of Agriculture to review the agency's 5.5 million acres of primitive areas, and the Secretary of the Interior to evaluate the wilderness potential of National Park System and National Wildlife Refuge System lands. The 90 th Congress began expanding the Wilderness System in 1968, as shown in Table 1 . The Wilderness System now contains 765 wilderness areas, with approximately 109.9 million acres in 44 states and Puerto Rico, managed by the four federal land-management agencies, as shown in Table 2 . An area of wilderness is further defined to mean ... an area of undeveloped Federal land retaining its primeval character and influence, without permanent improvements or human habitation, which is protected and managed so as to preserve its natural conditions and which (1) generally appears to have been affected primarily by the forces of nature, with the imprint of man's work substantially unnoticeable; (2) has outstanding opportunities for solitude or a primitive and unconfined type of recreation; (3) has at least five thousand acres of land or is of sufficient size as to make practicable its preservation and use in an unimpaired condition; and (4) may also contain ecological, geological, or other features of scientific, educational, scenic, or historical value. These imprecise criteria stem in part from differing perceptions of what constitutes wilderness. Thus, there are contrasting views about what constitutes wilderness and how wilderness should be managed. However, in response to concern that designating wilderness areas would restrict management of adjoining federal lands, language in many subsequent wilderness bills has prohibited buffer zones that would limit uses and activities on federal lands around the wilderness areas. Many of the wilderness statutes have directed the agencies to review the wilderness potential of certain lands and present recommendations regarding wilderness designations to the President and to Congress. Prohibited Uses

The Wilderness Act, directly and by cross-reference in virtually all subsequent wilderness statutes, generally prohibits commercial activities; motorized uses; and roads, structures, and facilities in designated wilderness areas. Continued motorized access and livestock grazing have also generally been permitted where they had been occurring prior to the area's designation as wilderness, as discussed above. Questions and discussions persist over the protection and management of these areas, which some believe should be designated as wilderness and others believe should be available for development. Just over half (52%) of this land—57.4 million acres—is in Alaska, and includes most of the wilderness areas managed by NPS (75%), FWS (90%), and FS (16%).
Congress enacted the Wilderness Act in 1964. This act created the National Wilderness Preservation System, reserved to Congress the authority to designate wilderness areas, and directed the Secretaries of Agriculture and of the Interior to review certain lands for their wilderness potential. The act also designated 54 wilderness areas with 9 million acres of federal land. Congress began expanding the Wilderness System in 1968, and today, there are 765 wilderness areas, totaling nearly 110 million acres, in 44 states. Numerous bills to designate additional areas and to expand existing ones have been introduced and considered in every Congress.
The Wilderness Act defined wilderness as an area of undeveloped federal land, among other criteria, but due to differing perceptions of wilderness and its purpose, it did not establish criteria or standards to determine whether an area should be designated. In general, wilderness areas are undeveloped, and commercial activities, motorized access, and roads, structures, and facilities are prohibited in wilderness areas. In response to conflicting demands, however, Congress has granted both general exemptions and specific exceptions to the general standards and prohibitions. Questions also persist over the frequency and extent to which federal agencies must review the wilderness potential of their lands, and how those lands should be managed.
Wilderness designation can be controversial. Because the designation generally prohibits commercial activities, motorized access, and human infrastructure from wilderness areas, opponents see such designations as preventing certain uses and potential economic development in rural areas where such opportunities are relatively limited. Advocates propose wilderness designations to preserve the generally undeveloped conditions of the areas.
The federal government owns about 28% of the land in the United States, although the proportion in each state varies widely. Four federal agencies—the Bureau of Land Management, National Park Service, and Fish and Wildlife Service in the Department of the Interior; and the Forest Service in the Department of Agriculture—manage most of the 110 million acres of designated wilderness, as well as many other lands. They also protect certain other lands as possible additions to the Wilderness System, and review the wilderness potential of lands.
In total, nearly 18% of federal land administered by the four major federal land management agencies, and nearly 5% of all land in the United States, has been designated as wilderness, largely in Alaska. Alaska, because of its size and relatively pristine condition, dominates wilderness statistics—more than 52% of designated wilderness is in Alaska (57.4 million acres). In total, nearly 16% of the entire state of Alaska has been designated as wilderness. In contrast, 3% of all land in the United States outside Alaska has been designated as wilderness.