The creation ofcomplex computer-based instructional systems is a relatively novel activity-one in which design is often an unexamined, poorly defined process. Careful analyses of how this design process actually occurs, and how it might be improved, are rare. This might seem surprising, given the multitude of instructional design models and courseware production tools that abound, and the availability of several texts that offer guidance to the courseware producer. Nevertheless, it is clear that:

1. The range of different types of complex, interactive, computer-based systems that are created in order to support learning is very great-much greater than the established instructional design (ID) models and courseware authoring tools can claim to deal with. Although we have the beginnings of a research literature on learning with some of the more popular types of instructional com"puting systems-such as simulations, hypermedia systems, modeling tools, or collaborative learning environments-we have very little principled guidance that can be used in the design of such systems.