Historic districts in the United States are designated historic districts recognizing a group of buildings, archaeological resources, or other properties as historically or architecturally significant. Buildings, structures, objects, and sites within a historic district are normally divided into two categories, contributing and non-contributing. Districts vary greatly in size and composition: a historic district could comprise an entire neighborhood with hundreds of buildings, or a smaller area with just one or a few resources.

In the law regulating historic districts in the United States, a contributing property or contributing resource is any building, object, or structure which adds to the historical integrity or architectural qualities that make the historic district significant. Government agencies, at the state, national, and local level in the United States, have differing definitions of what constitutes a contributing property but there are common characteristics. Local laws often regulate the changes that can be made to contributing structures within designated historic districts. The first local ordinances dealing with the alteration of buildings within historic districts was enacted in Charleston, South Carolina in 1931.