Silverlight 3 provides validation mechanism while using Two-Way data binding. Silverlight 3 also provides default a Validation Exception UI – callout with exception details, which could be customized. Many input-related controls such as TextBox, CheckBox, etc. have built-in support for validation. How to use? Simple, like everything with Silverlight: To enable validation, use the ValidatesOnExceptions property. < TextBox Text ="{ Binding ID , Mode =TwoWay, ValidatesOnExceptions =True}"...