The National Park Service Act, passed in 1916, established the National Park Service in the United States.  The Park Service is a part of the U.S. Department of the Interior, and its purpose is to preserve nature for future generations.  It was the first agency of this sort in the world.

The Act was passed because of lack of uniformity and guidelines in the forming and managing of U.S. national parks.  The National Park Service began by assuming responsibility for 14 parks and 21 national monuments.  Stephan Mather was the Park Service's first director and Horace Albright was his assistant.

Immediately, Mather and Albright worked to gain public support and protection of their system by emphasizing tourism as a large element of the parks, and in this they were hugely successful.  Indeed, it was not long before the Park Service faced the issue of preservation versus enjoyment -- an issue that came to the fore as tourism became destructive to the parks through overcrowding and pollution.  The Park Service has since tried to deal with these problems, striving for the middle ground between conservation and pleasure.

The National Park Service currently has under its administration 355 sites, totaling 80 million acres in 49 states, including 50 national parks, 79 National Monuments, 69 National Historic Sites, and 29 National Historical Sites.  There are a total of 22 such categories, covering everything from rivers to the White House.