This book addresses the need to develop environmentally friendly living spaces. The growing interest in energy conservation has led to studies on the overall performance of buildings, with respect to their environment. Mexico does not yet have standards that consider the specific requirements of different climatic regions. The windows strongly condition the balance between the provision of natural light and the reduction of solar gains in buildings. However, its design has been governed by intuitive and aesthetic criteria, wasting their capacity as light sources and their benefits in reducing electricity consumption. Today it is possible to propose guidelines, through local climate assessments, that consider annual light and energy conditions; these are done with computational simulation tools and algorithms. The main objective of this work is to provide window design criteria that fit the needs of the different climatic regions of Mexico.