The National Park System of the United States of America comprises 391 areas covering more than 84 million acres in every state (except Delaware), the District of Columbia, American Samoa, Guam, Puerto Rico, and the Virgin Islands. These areas include national parks, monuments, battlefields, military parks, historical parks, historic sites, lakeshores, seashores, recreation areas, scenic rivers and trails, and the White House.

One of the first people generally credited with conceptualizing a "national park" was George Catlin (1796-1872).On a trip to the Dakotas in 1832, he worried about the impact of America's westward expansion on Indian civilization, wildlife, and wilderness. They might be preserved, he wrote, "by some great protecting policy of government . . . in a magnificent park . . . . A nation's park, containing man and beast, in all the wild and freshness of their nature's beauty!"

The idea had gained some acceptance years later, when in 1864 Congress donated Yosemite Valley to California for preservation as a state park. There was still no real system of national parks in the United States until August 25, 1916, when President Woodrow Wilson signed the Organic Act creating the National Park Service (NPS). Established under the umbrella of the Department of the Interior, the NPS was responsible for protecting the 40 national parks and monuments then in existence.

An Executive Order in 1933 transferred 63 national monuments and military sites from the Forest Service and the War Department to the National Park Service. This action was a major step in the development of today's truly national system of parks-a system that includes areas of historical, cultural, scientific, and scenic importance.

In 1970, Congress declared in the General Authorities Act that all units of the system have equal legal standing in a national system. Additions to the National Park System are now generally made through acts of Congress, and national parks can be created only through such acts. But the President has authority, under the Antiquities Act of 1906, to proclaim national monuments on lands already under federal jurisdiction.