XAML Triggers

There are three types of triggers in WPF: Property, Data and Event.
A property trigger is invoked when the value of a dependency property changes.
A data trigger is invoked when the value of a .NET property changes.
An event trigger is invoked when a routed event is raised.

Here is an example of a property based trigger:
<Style TargetType="{x:Type Button}" key="TriggerStyle">
  <Style.Triggers>
   <Trigger Property="IsMouseOver" value="True">
      <Setter Property="Background" Value="Green">
    </Trigger>
  </Style.Triggers>
</Style>

Here is an example of an event based trigger:
<Button Name="btn_OK" Click="btnOK_Click">OK</Button>