Chapters 4 and 5 were both instances of greenfield development. In truth, that kind of development is relatively rare. Most of the time you, as an architect, will be working on evolving an existing system rather than creating one from scratch. In this chapter, we present an example of using ADD 3.0 for a brownfield system in a mature domain (as discussed in Section 3.3.3). We first present the business context and then examine the project’s existing architectural documentation. This is followed by a step-by-step summary of the activities that are performed during the ADD iterations to evolve the system. While this is a real system, some of the details have been changed to protect the identities of the actors.