In the XAML below the ToolTip correctly binds to RelativeSource Self. However, I can't for the life of me work out how to get the TextBlock in the commented block to refer to SelectedItem.Description <Controls:RadComboBoxWithCommand x:Name="cmbPacking" Grid.Row="2" Grid.Column="5" ItemsSource="{Binding PackingComboSource}" DisplayMemberPath="DisplayMember" SelectedValuePath="SelectedValue" SelectedValue="{Binding ElementName=dataGrid1, Path=SelectedItem.PackingID}" ToolTip="{Binding RelativeSource={RelativeSource Self}, Path=SelectedItem.Description}" IsSynchronizedWithCurrentItem="True" Style="{StaticResource comboBox}"> <!-- <Controls:RadComboBoxWithCommand.ToolTip>--> <!-- <TextBlock Text="{Binding RelativeSource={RelativeSource Self}, Path=SelectedItem.Description}" TextWrapping="Wrap" Width="50"/>--> <!-- </Controls:RadComboBoxWithCommand.ToolTip>--> </Controls:RadComboBoxWithCommand> I would appreciate any suggestions Thanks - Jeremy