This last chapter of the book takes up the issue of how to separate a program’s computation-related responsibilities from its presentation-related ones. It argues that programs should isolate the computation classes from the presentation classes, and for this you need classes to mediate between them. The computation, presentation, and mediator classes are called model, view, and controller. This chapter introduces the MVC pattern, which is the preferred way to organize these classes in a program. The chapter discusses the advantages of using the MVC pattern and gives several examples.