I was just about to ask here, and then Googled it and found the answer...

How do you PRINT a WPF window?

It's crazy simple...

        private void btnPrint_Click(object sender, RoutedEventArgs e)
        {
            PrintDialog prtDlg = new PrintDialog();
            if(prtDlg.ShowDialog() == true)
            {
                prtDlg.PrintVisual(ElementNameHere, "Title Here");  // The Name you call the Window in the XAML file
            }
        }

You can also send just a Canvas, or a ListView, or any single element or container that you can provide the name of.

Here are the links where I found this very helpful info:

http://itknowledgeexchange.techtarget.com/wpf/printing-with-wpf/
http://itknowledgeexchange.techtarget.com/wpf/wpf-printing-using-printvisual/
http://itknowledgeexchange.techtarget.com/wpf/wpf-printing-why-is-it-small/
http://itknowledgeexchange.techtarget.com/wpf/wpf-printing-use-the-printing-page/
http://itknowledgeexchange.techtarget.com/wpf/wpf-printing-documents/
http://itknowledgeexchange.techtarget.com/wpf/wpf-problems-printing-documents/