~ ~ In order to build an Intelligent Computer-Aided Design (IntCAD) tool, a domain needed to be selected and defined. This is because a general purpose CAD tool would be beyond the scope of a master's thesis. In this chapter, the requirements of the design system and reasons for those requirements are discussed. Then the choice of tower design as the domain is detailed. The sections following that show how this domain meets the requirements set forth. The user's and system's functions are discussed. The last part of the chapter discusses the various agents which can be built for this domain.