From the National Trust for Historic Preservation:

For property owners looking to permanently protect their historic properties, one of the most effective legal tools available is the preservation easement - a private legal interest conveyed by a property owner to a preservation organization or to a government entity. The decision to donate a preservation easement is almost always voluntary, but, once made, it binds both the current owner and future owners to protect the historic character of the property subject to the easement.

Preservation easements have been used to protect a wide range of historic properties across the country - from New England Cape Cod cottages to Southwestern archaeological sites, and from Kentucky horse farms to mid-twentieth century Modernist houses in California. While some easements are for a period of years, in most instances easements are created as permanent restrictions.

The donation of preservation easements to qualified easement-holding organizations can provide useful tax benefits to donors, but the tax benefits will vary considerably, from property to property and from easement to easement. Property owners should be wary of any promotion suggesting a standard formula for deductions, or implying that donors can reap significant tax benefits from easements that do not significantly reduce the value of their property. And prospective easement donors should take seriously recent statements by the IRS that it plans to look carefully at whether some taxpayers are taking appropriate deductions for easement donations.

Additional information on preservation easements can be obtained at the National Trust for Historic Preservation's website: Preservation Easements: An Important Legal Tool for the Preservation of Historic Places.