This paper proposes a validated and integrated calculation procedure for the prediction of solar spectra incident on vertical (or otherwise tilted) windows as a function of local climatic conditions in North America or@ ultimately@ any site in the world. This procedure is aimed at engineers with a modest background in meteorology@ climatology@ or atmospheric sciences and@ therefore@ tries to reconcile accuracy@ flexibility@ and ease of use. The procedure is backed by a thorough literature review and detailed performance assessment. The spectral radiationmodel (SMARTS) finally selected for its capabilities and performance (among other factors) is not based on any empirical relationship. It is capable of predicting spectral and broadband irradiates@ as well as illuminance under cloudless skies at any location where the required inputs are available. The accuracy of the product spectra is comparable to that from to that from state-of-art rigorous atmospheric models or from the best instruments. Such accurate results can only be obtained if a precise description of the atmospheric conditions is input to the model. A detailed methodology is described to obtain the basis atmospheric variables for any location in North America. It is anticipated that the current improvements in remote sensing from satellites will provide the means to extend the method to any site in the world. To illustrate the method@ an example of application is provided for the various facades of the ASHRAE headquarters in Atlanta. Substantial improvements in the calculation of solar heat gains through spectral selective fenestration and the resulting colling loads in buildings are the ultimate benefits expected from the procedure.