<Button>
  <TextBlock>Hey <Bold>you</Bold>!!!</TextBlock>
</Button>

<Button>
  <Button.Content>
    <TextBlock>Hey <Bold>you</Bold>!!!</TextBlock>
  </Button.Content>
</Button>

<Grid>
   <Button Name="button1" Width="40" Height="40"
           Content="something" FontWeight="Bold" />
</Grid>

private void ButtonClick(object sender, RoutedEventArgs e)
 {
     string buttonText = ((Button)sender).Content.ToString();
 }