WPF TextBlock Underline

You should use the property "TextDecorations" of the TextBlock. Like that:

 <TextBlock Text="H" TextDecorations="Underline"/>

Just to add my 2 cents, The same effect as Talia's answer can be achieved at runtime through this code:

YourTextBlock.TextDecorations = System.Windows.TextDecorations.Underline;

For some reason VS2010 doesn't show Intellisense for the RHS, but it compiles and runs correctly.

        <TextBlock VerticalAlignment="Bottom" 
                   HorizontalAlignment="Center" 
                   Margin="40" 
                   Height="40" 
                   FontSize="16" 
                   Tapped="TextBlock_Tapped"
                   Text="Text"
                   Foreground="{StaticResource LightBlue}">
            <Underline>
                <Run Text="Text"/>
            </Underline>
        </TextBlock>