This paper describes the development of a new concept for analyzing the performance of fenestration systems. We show the derivation of five indicators that can be combined in a variety of ways so that both qualitative and quantitative judgements can be made regarding total fenestration performance. The five indices consist of three related to energy: fuel (heating), electric (cooling), and peak electric demand; and two to comfort: thermal and visual. Performance comparisons of different systems are made possible by introduction of a non-dimensional user-defined weighting function that specifies the relationship between the five indices. A "figure of merit" is then calculated by combining the index values and weighting factors to provide a direct comparison between fenestration systems. The indices were derived by performing a multiple regression of several thousand hour-by-hour building heat transfer simulations of a prototypical office building module using the DOE-2 simulation program. From this regression analysis, we derived a series of simplified algebraic expressions that related fenestration performance to configuration variables. We then incorporated this methodology as the computational engine within a prototype fenestration design tool on a microcomputer using "hypermedia" concepts for the user interface. A "hypermedia" environment is one that integrates computer graphics, video, sound, animation, etc. with calculation sequences. This first prototype represents a significant developmental step toward our longterm goal of an overall building envelope design tool.