Building construction and operation have an enormous direct and indirect impact on the environment. While the definition of what constitutes sustainable building design is constantly changing, there are fundamental principles that nearly everyone agrees on: Optimize energy use, protect and conserve water, use environmentally preferable products, optimize operational and maintenance practices, and last but not least enhance indoor environmental quality. Going through a checklist obviously does not replace good design. However, a good designer will use the tools available to him or her appropriately, including energy and daylight modeling, thermal comfort analysis, experience, intuition, etc., to determine how they are best used to serve the purpose of re-integrating our built environment and ourselves with nature. Our intent in this paper is to focus on daylight modeling in buildings since it has always been difficult for practitioners and specially architects to handle this constantly changing dimension. Indeed, daylight moves, changes character, and varies with the weather. As an ecosystem service, it can provide buildings a living quality unachievable with any other design element and is a powerful vehicle of architectural expression.