Put Run block to TextBlock
<UserControl x:Class='SilverlightApplication3.MainPage' xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation' xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml' xmlns:d='http://schemas.microsoft.com/expression/blend/2008' xmlns:mc='http://schemas.openxmlformats.org/markup-compatibility/2006' mc:Ignorable='d' d:DesignWidth='640' d:DesignHeight='480'> <Canvas x:Name="LayoutRoot" Background="White"> <Border BorderBrush="Black" BorderThickness="1" Canvas.Left="20" Canvas.Top="20"> <TextBlock Text="This is text that does not wrap"/> </Border> <Border BorderBrush="Black" BorderThickness="1" Canvas.Left="20" Canvas.Top="60"> <TextBlock Text="This is text that wraps" TextWrapping="Wrap" Width="100"/> </Border> <Border BorderBrush="Black" BorderThickness="1" Canvas.Left="20" Canvas.Top="130"> <TextBlock> <Run FontSize="20" Text="This"/> <Run FontSize="20" FontStyle="Italic" Text="is "/> <Run FontSize="20" Text="text within a single"/> <LineBreak/> <Run Foreground="Red" FontSize="14" Text="TextBlock control."/> </TextBlock> </Border> </Canvas> </UserControl>