How do I implement a chromeless window with WPF?

Check out this blog post on kirupa.

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" WindowStyle="None" ResizeMode="NoResize">
    <Button HorizontalAlignment="Right" Name="button1" VerticalAlignment="Top" >Close</Button>
</Window>

You'll pretty much have to roll your own Close button, but you can hide the window chrome completely using the WindowStyle attribute, like this:

<Window WindowStyle="None">

That will still have a resize border. If you want to make the window non-resizable then add ResizeMode="NoResize" to the declaration.