The National Trails System is a series of trails in the United States designated "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". There are four types of trails: the national scenic trails, national historic trails, national recreation trails, and connecting or side trails. The national trails provide opportunities for hiking and historic education, as well as horseback riding, biking, camping, scenic driving, water sports, and other activities. The National Trails System consists of 11 national scenic trails, 21 national historic trails, over 1,300 national recreation trails, and seven connecting and side trails, as well as one national geologic trail, with a total length of more than 91,000 mi (150,000 km). The scenic and historic trails are in every state, and Virginia and Wyoming have the most running through them, with six.

Hiking is a long, vigorous walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century. Religious pilgrimages have existed much longer but they involve walking long distances for a spiritual purpose associated with specific religions.