Hiking is an outdoor activity which consists of walking in natural environments, often in mountainous or other scenic terrain. People often hike on hiking trails. It is such a popular activity that there are numerous hiking organizations worldwide. The health benefits of different types of hiking have been confirmed in studies. Some of the health benefits of hiking include, but are not limited to, losing excess pounds, decreasing hypertension, and improving mental health. The word hiking is understood in all English-speaking countries, but there are differences in usage.

In the United States and United Kingdom, hiking refers to walking outdoors on a trail for recreational purposes. A day hike refers to a hike that can be completed in a single day - not requiring an overnight camp. Multi-day hikes with camping is referred to as backpacking. In the United Kingdom hiking is usually called rambling, which resulted in the hiking organization named Ramblers. Bushwhacking specifically refers to difficult walking through dense forest, undergrowth, or bushes, where forward progress requires pushing vegetation aside. In extreme cases of bushwhacking where the vegetation is so dense that human passage is impeded, a machete is used to clear a pathway. Australians use the term bushwalking for both on- and off-trail hiking. New Zealanders use tramping (particularly for overnight and longer trips), walking or bushwalking. Multi-day hiking in the mountainous regions of India, Pakistan, Nepal, North America, South America, and in the highlands of East Africa is also called trekking. Hiking a long-distance trail from end-to-end is also referred to as trekking and as thru-hiking in some places. Examples of long-distance trails include the Appalachian Trail (AT) and Long Trail (LT).

Andrew Skurka is a professional backpacker who is best known for his two long-distance hiking firsts—the 6,875-mile Great Western Loop and the 7,778-mile Sea-to-Sea Route. He was named the 2007 "Adventurer of the Year" by National Geographic Adventure (which described him as "a Gen Y version of Henry David Thoreau or John Muir") and the 2005 "Person of the Year" by Backpacker Magazine.

In November 2007, Skurka completed the Great Western Loop, a 6,875-mile journey that links together 5 long-distance hiking trails, 12 National Parks, and over 75 wilderness areas, which he hiked in 208 days, an average of 33 miles per day. In addition, in July 2005 Skurka completed the Sea-to-Sea Route, a transcontinental network of long-distance hiking trails from Quebec to Washington, which took him 11 months and which involved 1,400 miles of snowshoeing. Skurka's shorter hikes include the 1,700-mile California section of the Pacific Crest Trail (in 44 days), the 480-mile Colorado Trail (twice), the 2,170-mile Appalachian Trail (in 95 days), a 385-mile trek through northern Minnesota in January, and many week and weekend-long trips in Colorado, Montana, and Wyoming. In 2010 he hiked a 4,679 mile route around Alaska, which took him 176 days.

John Muir (21 April 1838 – 24 December 1914) was a Scottish-born American naturalist, author, and early advocate of preservation of wilderness in the United States. His letters, essays, and books telling of his adventures in nature, especially in the Sierra Nevada mountains of California, have been read by millions. His activism helped to save the Yosemite Valley, Sequoia National Park and other wilderness areas. The Sierra Club, which he founded, is now one of the most important conservation organizations in the United States. One of the most well-known hiking trails in the U.S., the 211-mile (340 km) John Muir Trail, was named in his honor. Other places named in his honor are Muir Woods National Monument, Muir Beach, John Muir College, Mount Muir, Camp Muir and Muir Glacier.

In his later life, Muir devoted most of his time to the preservation of the Western forests. He petitioned the U.S. Congress for the National Park bill that was passed in 1890, establishing both Yosemite and Sequoia National Parks. Because of the spiritual quality and enthusiasm toward nature expressed in his writings, he was able to inspire readers, including presidents and congressmen, to take action to help preserve large nature areas. He is today referred to as the "Father of the National Parks," and the National Park Service produced a short documentary on his life.