The National Register of Historic Places structure number is an identifier for a building in the United States of America which is deemed worthy of preservation as part of the national historic or architectural patrimony.

The register is kept by the National Park Service, and a listing is a federal recognition rather than a local protection: it records significance and does not by itself prevent alteration or demolition.

Multiple structures can share the same number, because in many cases groups of structures or entire districts are joined in one NRHP record. A number on a building therefore does not always mean the building was listed in its own right.

The reverse also happens. A structure inside a listed historic district is covered by the district record and has no number of its own, so an empty field is not evidence that a building is unlisted.