A few Web Forms control expose the AutoPostBack property, which makes it possible to start a postback when the user clicks on these controls or changes their contents. By default this property is False, but you can set it to True for the following controls: TextBox, CheckBox, RadioButton, CheckBoxList, RadioButtonList, DropDownList, and ListBox.

A little known problem of this property is that it works thanks to a client-side piece of JavaScript code, therefore your application won’t work correctly if the end user has disabled client-side scripting on her browsers. For this reason you should make it clear that client-side scripts must be enabled to make your app work correctly. Even better, you might opt to provide a Submit button for those (few) users who have disabled this feature.