MVC and MVVM are key architectural constructs that we need to firmly understand before starting on a new project. Given that they're so embedded in Ext JS, it's even more important to have a good grasp of the ideas behind them and why implementing such patterns will assist in the way we construct our code base. In the next chapter, we'll move on to more practical examples of structuring an Ext JS application, incorporating MVVM concepts with a variety of other ideas that set out a strong platform to build on.