A historic structure is a building, feature, or overall development that has been officially designated as having significant historical, cultural, archaeological, or architectural value and is therefore afforded special protections under the law. While buildings and other structures may be considered historic on a smaller or local level, structures must meet the criteria established by the National Register of Historic Places to be considered national historic landmarks. This qualifies them for greater recognition and potential financial support for maintenance and renovation efforts, as well as for public access.

To be officially recognized as a national historic landmark, the structure must meet one of four main criteria, outlined by the National Park Service:

(1) a structure is associated with events that have made a lasting impact on the course of American history;

(2) a structure is associated with the life of an important person in American history;

(3) a structure embodies the distinctive characteristics of an architectural type, time period, or method of construction, or

(4) a structure may yield important information about prehistoric or historic cultures or events.

In order to be considered a historic structure, structures must meet one of these criteria and they must be properly documented in the official record of the National Register of Historic Places. Historic structures can include bridges, highways, canals, ships, and mines, as well as constructed buildings such as churches, courthouses, and civic centers.

Preserving historic structures is an important part of American history and culture, and the National Park Service has taken a leading role in preserving and promoting these places for visitors. National historic landmarks not only provide a tangible connection to our important past, but also serve as an important educational tool. Visitors from around the country and around the world can come to sites and learn about how our nation's culture and values evolved over time. They often represent an important reminder of how far we have come over the years, and can offer both inspiration and hope for the future.