In order to oversee the effect of historic building legislation, whose main intent is to control change, the Historic Buildings and Monuments Commission for England is operating a computerized monitor of all listed buildings (over one million) in metropolitan London. The first part is a formalized description of the buildings, making it possible to analyze their characteristics (such as date, use, form, scale, construction and materials, etc.). The second part is a formalized description of alterations; this includes the nature and type of change, and an assessment of the severity of its effect on the special interest of the building. It is also designed to have a direct effect on the day to day administration of historic buildings. Thus the monitor: 1) ensures that historic building controls are applied consistently; 2) identifies target areas so that limited resources can be deployed effectively; and 3) permits the creation and implementation of policy and strategy.