<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="TextDecorationExample.Window1" Title="TextDecoration Example" Width="720" Height="400"> <StackPanel> <TextBlock FontSize="24" Width="180" VerticalAlignment="Center">The lazy dog <TextBlock.TextDecorations> <TextDecoration Location="Underline" PenThicknessUnit="FontRecommended"> <TextDecoration.Pen> <Pen Brush="Red" Thickness="1" /> </TextDecoration.Pen> </TextDecoration> </TextBlock.TextDecorations> </TextBlock> </StackPanel> </Window>