What’s the difference between preservation, rehabilitation, and restoration, and reconstruction?

These four approaches to historic buildings are defined in the Secretary of the Interior’s Standards for the Treatment of Historic Properties.

Preservation: places a high premium on the retention of all historic fabric through conservation, maintenance, and repair. It respects a building’s continuum over time, and through successive occupancies, and the respectful changes and alterations that are made.

Rehabilitation: emphasizes the retention and repair of historic materials, but more latitude is provided for replacement because it is assumed the property is more deteriorated prior to work.

Restoration: focuses on the retention of materials from the most significant time in a property’s history, while permitting the removal of materials from other periods.

Reconstruction: establishes limited opportunities to re-create a non-surviving site, landscape, building, structure, or object in all new materials.

Source: National Park Service: The Secretary of the Interior’s Standards for the Treatment of Historic Properties, Introduction ” Choosing an Appropriate Treatment for the Historic Building”
http://www2.cr.nps.gov/tps/standguide/overview/choose_treat.html

see also: Introduction: Using the Standards and Guidelines for a Preservation, Rehabilitation, Restoration, or Reconstruction Project.”
http://www2.cr.nps.gov/tps/standguide/overview/using_standguide.html

Another excellent source for information on this topic is the Historic Preservation Services, National Park Service, Technical Preservation Services for Historic Buildings:

Secretary of the Interior’s Standards for the Treatment of Historic Properties
http://www2.cr.nps.gov/tps/secstan4.html
This source provides helpful information for choosing a treatment and the scope of work involved in each.