The Appalachian National Scenic Trail, generally known as the Appalachian Trail or simply the A.T., is a marked hiking trail in the Eastern United States extending between Springer Mountain in Georgia and Mount Katahdin in Maine. The trail is about 2,200 miles (3,500 km) long, though the exact length changes over time as parts are modified or rerouted. The Appalachian Trail Conservancy describes the Appalachian Trail as the longest hiking-only trail in the world. More than 2 million people are said to take a hike on part of the trail at least once each year.
The idea of the Appalachian Trail came about in 1921. The trail itself was completed in 1937 after more than a decade of work, although improvements and changes continue. It is maintained by 31 trail clubs and multiple partnerships, and managed by the National Park Service, United States Forest Service, and the nonprofit Appalachian Trail Conservancy. Most of the trail is in forest or wild lands, although some portions traverse towns, roads and farms. It passes through 14 states: Georgia, North Carolina, Tennessee, Virginia, West Virginia, Maryland, Pennsylvania, New Jersey, New York, Connecticut, Massachusetts, Vermont, New Hampshire, and Maine.
Thru-hikers attempt to hike the trail in its entirety in a single season. The number of thru-hikes per year has increased steadily, with 715 northbound and 133 southbound thru-hikes reported for 2017. Many books, documentaries, websites, and fan organizations are dedicated to the pursuit. Some hike from one end to the other, then turn around and thru-hike the trail the other way, known as a "yo-yo".
An extension known as the International Appalachian Trail continues northeast, crossing Maine and cutting through Canada to Newfoundland, with sections continuing in Greenland, through Europe, and into Morocco. Other separate extensions continue the southern end of the Appalachian range in Alabama and continue south into Florida, creating what is known as the Eastern Continental Trail.
The Appalachian Trail, the Continental Divide Trail, and the Pacific Crest Trail form what is known as the Triple Crown of Hiking in the United States.