Preservationists use a common language that had its beginnings in the National Historic Preservation Act of 1966. This act created the Secretary of the Interior's Standards for the Treatment of Historic Properties, which defined the terms and treatments that have become the standard for preservation projects and plans. These terms have been used in many of the preservation plans developed for the Getty Foundation's Campus Heritage Initiative. The Standards for the Treatment of Historic Properties define characteristics for each of four treatment approaches: preservation, rehabilitation, restoration, and reconstruction. The National Register of Historic Places is a listing of cultural resources that have been deemed to be significant. Nationally significant resources with a high degree of integrity may be listed as National Historic Landmarks. Authors and researchers of the campus heritage plans used many sources for historical information about buildings and landscapes. The National Register of Historic Places and National Historic Landmarks databases include photographs and written reports of listed properties. State Historic Preservation Offices (SHPOs) were also useful resources for gathering building and landscape information for heritage plans. The Campus Heritage Initiative plans, as a group, are made even more valuable through the consistency of terms and research resources.