Revision with unchanged content. This book recognizes the need for building simulation/performance tools that can easily be integrated into the building design process. It provides a background about the current state of simulation tools & attempts to find reasons of their non-usage by building designers/architects. Findings confirm that the complexity of simulation tools created by scientists, who are more technically oriented, discourages use by architects who are more visually oriented people. The research is limited to the interface design of the new front-end Integrated Building Design Information Interface (IBDII), that allows designers to make more informed decisions during the design process & permits a user interface where the mode of input is graphical and not numerical. Criteria for the new front-end interface enable the development of a series of mock-up interface designs that are responsive to the needs of architects, & graphical user interface (GUI) design principles are considered. A working GUI of the IBDII prototype is created and is then put through an empirical user testing. This Usability Testing establishes the usefulness, effectiveness, likeability and learnability of IBDII and provides suggestions for future developments. The testing evaluation ascertains that the interface is easy to learn and use.