The National Wild and Scenic Rivers System was created by the Wild and Scenic Rivers Act of 1968 (Public Law 90-542), enacted by the U.S. Congress to preserve certain rivers with outstanding natural, cultural, and recreational values in a free-flowing condition for the enjoyment of present and future generations.

The Act is notable for safeguarding the special character of these rivers, while also recognizing the potential for their appropriate use and development. It encourages river management that crosses political boundaries and promotes public participation in developing goals for river protection. The Act, signed into law by President Lyndon B. Johnson in the height of the United States environmental era, states:

"It is hereby declared to be the policy of the United States that certain selected rivers of the Nation which, with their immediate environments, possess outstandingly remarkable scenic, recreational, geologic, fish and wildlife, historic, cultural or other similar values, shall be preserved in free-flowing condition, and that they and their immediate environments shall be protected for the benefit and enjoyment of present and future generations. The Congress declares that the established national policy of dams and other construction at appropriate sections of the rivers of the United States needs to be complemented by a policy that would preserve other selected rivers or sections thereof in their free-flowing condition to protect the water quality of such rivers and to fulfill other vital national conservation purposes." (Wild & Scenic Rivers Act)

The Act established the National Wild and Scenic Rivers System to protect and enhance rivers found to be regionally and nationally significant. Rivers may be designated by Congress or, if certain requirements are met, the Secretary of the Interior. Each designated river is administered by either a federal, state, or tribal agency, or as a partnership between any number of these government entities and local NGOs. Designated segments need not include the entire river and may include headwaters and tributaries. For federally administered rivers, the designated boundaries generally average one-quarter mile on either bank in the lower 48 states and one-half mile on rivers outside national parks in Alaska in order to protect river-related values.

As of August 2018, the National System protects over 12,700 miles (20,400 km) of 209 rivers in 40 states and the Commonwealth of Puerto Rico; this is less than one-quarter of one percent of the nation's rivers, which flow over 3.5 million miles (5,600,000 kilometers) across the United States. By comparison, more than 75,000 large dams across the country have modified at least 600,000 miles (970,000 km), or about 17 percent of American rivers.