What's the difference between a Trigger and a DataTrigger?
A regular Trigger only responds to dependency properties.
A DataTrigger can be triggered by any .NET property (by setting its Binding property). However, its setters can still target only dependency properties.
Another difference is that a DataTrigger can be bound to another control, a StaticResource, etc etc.
<Style TargetType="TextBox"> <Style.Triggers> <DataTrigger Binding="{Binding SomeProperty, ElementName=someOtherControl" Value="Derp"> <!-- etc -->You can only examine the instance on which the style is set when using a Trigger. For example, a Trigger applied to a Button can inspect the value of IsPressed, but it would not be able to inspect the (for example) Text value of a TextBox on the same form if you wished to disable the Button if the TextBox was empty.
The short answer (as I'm about to sleep)- A trigger works on dependency properties (typically GUI properties) whereas data triggers can be triggered by any .NET property (typically a property in a ViewModel that implements INotifyPropertyChanged).