To date, the City of Portland has designated twelve local historic districts. Many of these historic districts are also listed in the National Register of Historic Places. Following is a list of Portland's historic districts, with links to detailed information on each district. ​

​Within each district, every building is assigned a classification according to its "preservation value": Landmark, Contributing, or Non-contributing. Alterations or additions to Landmark or Contributing structures are subject to review under the preservation ordinance's Standards for Review of Alterations. Alterations to non-contributing structures are also subject to review, however the review standards are less rigurous. Non-contributing structures may be demolished as of right, but any replacement construction is subject to review and approval under the ordinance's Standards for Review of Construction. Finally, new construction on undeveloped parcels within the district is subject to review under the ordinance's Standards for Review of Construction. See links (in the left hand margin) for more information on the review standards and application requirements.