From questions to answers via models: Answers to questions?

We all agree that systems are becoming far too complex to understand easily in their entirety and that abstraction is the key to managing such complexity. The techniques used in modeling provide abstractions which can answer key questions, so what are the questions about modeling that are left? In fact it often seems that there are more questions than answers. Put another way, modeling has been an important tool in many areas for four decades or more. Today sees renewed interest in the application of modeling to the understanding of enormously complex systems. Yet, there remain many challenges in making modeling accessible to non-specialists. This talk poses the questions which seem most meaningful at present and attempts to answer some of them. To provide a structure to this, we assume the key questions are essentially unchanged since computer based simulation began and examine how well we can now answer them.