The National Trails System was created by the National Trails System Act (Pub.L. 90–543, 82 Stat. 919, enacted October 2, 1968), codified at 16 U.S.C. § 1241 et seq.
The Act created a series of National trails "to promote the preservation of, public access to, travel within, and enjoyment and appreciation of the open-air, outdoor areas and historic resources of the Nation." Specifically, the Act authorized three types of trails: the National Scenic Trails, National Recreation Trails and connecting-and-side trails. The 1968 Act also created two national scenic trails: the Appalachian and the Pacific Crest; and requested that an additional fourteen trail routes be studied for possible inclusion.
In 1978, as a result of the study of trails that were most significant for their historic associations, a fourth category of trail was added: the National Historic Trails. Since 1968, over forty trail routes have been studied for inclusion in the system. Of these studied trails, twenty-one have been established as part of the system. Today, the National Trails System consists of 30 National Scenic and Historic Trails and over 1,000 National Recreation Trail and two connecting-and-side trails, with a total length of more than 50,000 miles (80,000 km). These National Trails are more than just for hiking, many are also open for horseback riding, mountain biking and camping.
As Congressionally established long-distance trails, each one is administered by a federal agency, either the Bureau of Land Management, United States Forest Service, or National Park Service. Two of the trails are jointly administered by the BLM and the NPS. Occasionally, these agencies acquire lands to protect key sites, resources and viewsheds. More often than not, they work in partnership with the states, local units of government, land trusts and private landowners, to protect lands and structures along these trails, enabling them to be accessible to the public. National Recreation Trails and connecting-and-side trails do not require Congressional action, but are recognized by actions of the Secretary of the Interior or the Secretary of Agriculture. All of the National Trails are supported by private non-profit organizations that work with the various federal agencies under the Partnership for the National Trails System (PNTS).