The National Register of Historic Places (NRHP) is the federal government's official list of districts, sites, buildings, structures, and objects deemed worthy of preservation. It is administered by the National Park Service. About 80,000 properties are individually listed on the National Register, and over a million are included as part of larger historical districts. Unless deemed "exceptionally significant," a property must be at least 50 years old to be listed.
Note this is not an exhaustive list of NRHP sites in and around Boston. It only includes the sites that are included in the AIA Guide.