The ProgressBar control is modeled after the native progress indicators used on Windows 8 to provide a modern user experience. It can display as an animated looping pattern of dots to indicate that an indeterminate operation is in progress.
The ProgressIndicator control gives you a more customizable way to visualize some indeterminate action. You can display a classic loading ring and provide a descriptive label for the user.
The progress controls don't block the UI thread from running, so you can show a progress indicator while the background UI is performing an operation.