All too often, the original windows are unnecessarily removed and replaced from historic buildings. In some instances, replacement is justified due to the extent of deterioration resulting from years of deferred or inappropriate maintenance. However, often historic windows are unnecessarily replaced as a result of incorrect assumptions or misinterpretation of their condition. Alternatively, a designer may believe that a new window will perform better, require less maintenance, increase energy efficiency, or just last longer than the existing original windows. This may not be the case. This paper will address issues related to the evaluation and restoration of historic wood and metal windows. An overview of the methodology used by the authors to evaluate the condition of windows and determine repairs that are necessary to maintain structural integrity, repairs that are necessary to address air and water infiltration, and repairs relative to aesthetics and function, will be presented.