<p>I change the FontSize of Text in a Style trigger, this causes the Control containing the text to resize as well. How can I change the Fontsize without affecting the parent's size? </p>

What kind of control are you using? If this is a HeaderedControl like a GroupBox or TabItem then you need to specifically set the HeaderTemplate like this:
```
```
<DataTemplate x:Key="MyHeaderTemplate">
  <TextBlock Text="{Binding}" Fontsize="14" FontWeight="Bold" />
</DataTemplate>
```
```