On the surface, this discussion of software process models may seem to be off-topic in a requirements text. Assuredly, it is not. In the move from a waterfall model to the iterative model, we can finally dispense with the notion that requirements are fully discoverable and can be fully documented before development begins and that they can be fixed or frozen thereafter. It was an interesting theory, and it appeared to make life for developers more straightforward as they imagined their work could be built on an unchanging foundation. Unfortunately, it simply did not work. Requirements change, and to pretend otherwise is, at best, foolish. We must understand that requirements discovery and requirements management are full lifecycle issues. The more we discover, the more we discover, and the better we understand the system to be built. With this context behind us, we can now move on to discovering that which we need to discover about our impending system. And we'll learn how to manage requirements change in a way that will augment, rather than destroy, the foundation for our development work.