A National Historic Landmark (NHL) is a building, district, site, structure, or object, almost always within the United States, officially recognized by the United States government for its historical significance. Landmarks are designated by the United States Secretary of the Interior because they are:

• Sites where events of national historical significance occurred;
• Places where prominent persons lived or worked;
• Icons of ideals that shaped the nation;
• Outstanding examples of design or construction;
• Places characterizing a way of life; or
• Archeological sites able to yield information.

A National Historic Landmark District (NHLD) is a historic district that is recognized as an NHL. It may include contributing structures or other elements, and non-contributing ones.

On October 9, 1960, 92 properties were announced as designated NHLs by Secretary Fred Andrew Seaton. The first of these was a political nomination, Sergeant Floyd Grave and Monument in Sioux City, Iowa. It was officially designated on June 30 of that year, but for various reasons the public announcement of the first several NHLs was delayed.

More than half of the National Historic Landmarks are privately owned. There are currently fewer than 2500 NHLs. The National Historic Landmarks Program relies on suggestions for new designations from the National Park Service, which also assists in maintaining the landmarks. A friends group of owners and managers, the National Historic Landmark Stewards Association, also works to preserve, protect and promote National Historic Landmarks.

If not already listed on the National Register of Historic Places, an NHL is automatically added to the Register upon designation. About three percent of Register listings are NHLs.