An historic district is an area with a distinctive character recalling a particular architectural or historical heritage. Currently, three such areas have been designated by City Council and therefore, come under the jurisdiction of the Historic District Ordinance. The City's authority to create historic districts stems from Pennsylvania state enabling legislation commonly referred to as Historic District Act No. 167, adopted in 1961. City Council adopted Allentown's Historic District Ordinance in September 1978, when it designated Old Allentown as the first of the City's three current districts. Since then, the Old Fairgrounds and, most recently, the West Park Historic Districts have been created.

The Ordinance was adopted to preserve the historic and architectural character of the exterior facades of structures in the historic districts. The ordinance does not require the restoration of homes to their original appearance, although many owners have chosen to do so. Rather, the ordinance requires that any exterior changes made to properties within the districts that can be seen from the public right-of-way be done in a manner that is in keeping with the architectural and historic character of the building and the district.

Guidelines are available for each of the districts to help property owners with their designs. Further, each change needs to be reviewed by either city staff or the Historic Architectural Review Board (HARB) to ensure its appropriateness.