Application and Page Lifecycle As I said in the introduction, one of the foundations required for a proper understanding of Windows Store applications are the concepts of application and page lifecycle. The lifecycle is particularly important in some of the design decisions that you make on how your application will behave when users first launch the app, as well as when they move on to other applications and then return. Further, you need to account for what happens when the system needs to shut down the app in the background. To make sense of what's happening during the lifecycles, you first must have an understanding of what some of the different ways the user, as well as the system, interact with Windows Store applications. Obviously, some of the time, the applications are started or activated by a user explicitly opening them. But there are other ways in Windows 8 of how these apps are started. The operating system makes the distinction between two different types of programmatic interaction with your app, which are extensions and contracts. Extensions are a way of extending Windows and allowing your application to tap into an array of extensibility points, of VOS. For instance, the protocol activation extension allows your application to register for a certain protocol scheme and launch when that scheme is run in the system. Contracts, on the other hand, are extensibility points between your application and other apps or the operating system. The contract behaves much like an interface in object oriented environments. The contract is an agreement by the source and the target to do things like share data, facilitate searching and the like. Now that you have some familiarity with extensions and contracts, the application lifecycle as a whole will make more sense in context.