Leave No Trace, sometimes written as LNT, is a set of ethics promoting conservation of the outdoors. Originating in the mid-20th century, the concept started as a movement in the United States in response to ecological damage caused by wilderness recreation. In 1994, the non-profit Leave No Trace Center for Outdoor Ethics was formed to create educational resources around LNT, and organized the framework of LNT into seven principles.

The idea behind the LNT principles is to leave the wilderness unchanged by human presence.

By the 1960s and 1970s, outdoor recreation was becoming more popular, following the creation of equipment such as synthetic tents and sleeping pads. A commercial interest in the outdoors increased the number of visitors to national parks, with the National Park Service seeing a five-fold increase between 1950 and 1970, from 33 million to 172 million. Articles were written about the wild being “loved to death,” problems with overcrowding and ecological damage, and the need for management. To solve this, regulations were imposed, including limits on group sizes and where camping was allowed. This was met negatively, with people writing that it took the joy and spontaneity out of wilderness recreation.

The focus was shifted towards education, with the National Park Service (NPS), United States Forest Service (USFS), and the Bureau of Land Management (BLM) training Wilderness Informational Specialists to teach visitors about minimal impact camping. In 1987, the three departments cooperatively developed a pamphlet titled "Leave No Trace Land Ethics".

At the same time, there was a cultural shift in outdoor ethics from woodcraft, where travelers prided themselves on their ability to use available natural resources, to having a minimal impact on the environment by traveling through wilderness as visitors. Groups such as the Sierra Club, the National Outdoor Leadership School (NOLS), and the Boy Scouts of America were advocating minimum impact camping techniques, and companies like REI and The North Face began sharing the movement.

In 1990, the national education program of Leave No Trace was developed by the USFS in conjunction with NOLS, alongside Smokey Bear, Woodsy Owl, and programs like Tread Lightly! geared towards motorized recreation. The Bureau of Land Management joined the program in 1993 followed by the National Park Service and U.S. Fish and Wildlife Service in 1994.

The number of LNT principles varied widely during the 1990s, starting from 75 and dropping to 6 as more people had input and principles were condensed. However, by 1999, the list was finalized as seven principles and has remained unchanged.

Since 1994, the Leave No Trace program has been managed by the Leave No Trace Center for Outdoor Ethics, a 501(c)(3) non-profit organization, dedicated to the responsible enjoyment and active stewardship of the outdoors worldwide. Leave No Trace works to build awareness, appreciation and respect for wildlands through education, research, volunteerism and partnerships. The center also has a youth education initiative, Leave No Trace for Every Kid, which emphasizes asset development in youth through the lens of outdoor stewardship.