Computer-aided-design (CAD) systems are now used to design all kinds of artifacts, from jet fighters to works of art. A major challenge in the design of a CAD system itself is the user interface (UI). Developing the UI to a CAD system raises myriad questions about input devices and techniques, display devices and techniques, and the details of the dialogue that relates the two. But these questions are ancillary to one central question: what is the fundamental nature of the interaction between human and computer in the design process supported by the CAD system? Is the design activity essentially manual, with the computer playing the role of  passive tool, like a pen or paintbrush? Or is the computer augmenting the human designer by actively restricting available design choices, or by playing the role of critic or “improver”? Or maybe the interaction paradigm is one of “interactive evolution,i in which  the computer is responsible for generating design alternatives, with the human merely choosing among choices suggested by the machine. Or perhaps the computer performs the design process completely automatically, with a final acceptance check being the only human contribution? The panelists will describe these different paradigms for human-computer cooperation in a set of related CAD systems and prototypes and discuss the conditions under which each paradigm might be most useful.