<Window x:Class="WpfApplication3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Calendar HorizontalAlignment="Left" Margin="160,74,0,0" 
                  SelectedDatesChanged="Calendar_SelectedDatesChanged"  VerticalAlignment="Top"/>
    </Grid>
</Window>

 private void Calendar_SelectedDatesChanged(object sender, SelectionChangedEventArgs e)
            {
                  var calendar = sender as Calendar;

                  if(calendar.SelectedDate.HasValue)
                        calendar.DisplayDate = calendar.SelectedDate.Value;
            }