We've covered a fair bit of material so far, and now seems like a good time to cover configuration changes. When an application is running on a device, and the device's configuration changes (for example, is rotated 90 degrees), your application needs to respond accordingly. The new configuration will most likely look different from the previous configuration. For example, switching from portrait to landscape mode means the screen went from being tall and narrow to being short and wide. The UI elements (buttons, text, lists, and so on) will need to be rearranged, resized, or even removed to accommodate the new configuration.