Anyone who has ever sat near a cold window on a winter day or in direct sunlight on a hot day recognizes that windows can cause thermal discomfort. In spite of this broad recognition there is no standard method to quantify the extent of such discomfort. The purpose of this study was to: 1. Review the literature to identify relevant work relating to windows and thermal comfort. 2. Develop an improved understanding of the impact of windows on thermal comfort and to propose an analytical method for evaluating this impact. The method could form the basis for a future NFRC window comfort rating method that could be used by both designers and consumers.