In recent years. researchers, designers and contractors have begun to investigate the use of new technologies in building construction and operation.The search for more efficient designs has led to complex and difficult to analyze components, systems, and whole building structures. Existing building energy simulation programs were initially conceived in an era when design questions were simpler than they are today. As a result, there are fundamental limitations in the analysis capabilities of these programs. In particular, techniques have not been developed that allow realistic simulation of the interactions between building envelope, architectural components and mechanical equipment and their controls in a generalized, integrated and easily extendible manner. Analysis of complex designs and advanced technologies requires superior capabilities of the next generation of building performance simulation programs. In five to ten years, the use of computer-aided design (CAD) systems for buildings will be commonplace; expert systems will be developed to improve decision making in architectural and engineering design and operational problems; and energy management systems will increasingly be used for building control, monitoring and diagnostics. The advanced building simulation programs will greatly facilitate the integration of performance simulation with design simulation, thus ensuring that energy efficiency and comfort evaluation issues receive proper emphasis in building design and control. Furthermore the integrated building systems will facilitate the creation of modularized, user-friendly and easy to operate programs for analysis of building components and their interactions. The author explores opportunities in building simulation advances and suggest ways to extend them into next generation of software programs for the A&E Service industry.