Engineering organizations developing large complex systems are usually not capable of determining an "overall optimal" system design. Rather, the system is divided in "com­ ponents" or subsystems (such as an axle in a car or a module in a software product), for each of which a performance can be measured, an optimal design can be found or at least approximated, and for which a designer (or engineer or team of engineers) is responsible. Each engineer then makes, at first, decisions to optimize "his" component. In real orga­ nizations, designers often develop considerable pride in the solutions they have found for their components. However, it is the very nature of complex systems that the components cannot be optimized in isolation, but that they interact in determining the quality of the overall system (via space constraints, or via the exchange of fluids, air, force, electricity, or information). To some degree, these interactions are known from experience and can be anticipated, or are embedded in accepted design principles. However, in any complex design project that is not entirely routine and marginal, many such interactions are not known at the outset.