Buildings account for 35 percent of the world''s energy use and a similar percentage of CO2 emissions. In order to ensure adequate energy supplies and to curtail the growth of CO2 emissions, it is essential that building energy consumption is significantly reduced. One way this can be achieved is through the introduction of sustainable building design enabled by innovative building simulation tools, for example the whole building heat, air and moisture (HAM) transfer model. The hygrothermal transfer between building envelopes and indoor air has a significant influence on the indoor environment and energy performance of buildings. However in most applications, building envelope designers attempt to predict the hygrothermal performance of an individual building element by uncoupling the system from interactions of the other envelope components to both indoor/outdoor environments. A more advanced building performance evaluation approach requires the direct coupling of all building envelope systems with HVAC systems and indoor/outdoor environments. The book will focus on the development of a coupled HAM model for whole building simulation.