How do I Add a Tooltip To a DataGridTextColumn

Yes, you can add tooltip text to DataGridTextColumn - just stylize it

<DataGridTextColumn Header="ScreenName" Binding="{Binding ScreenName}" >    <DataGridTextColumn.CellStyle>        <Style TargetType="DataGridCell">            <Setter Property="ToolTip" Value="{Binding Name}" />        </Style>    </DataGridTextColumn.CellStyle></DataGridTextColumn>

I'm not sure if you can add a tooltip to a DataGridTextColumn but you can easily use the DataGridTemplateColumn and the ToolTipService instead. e.g.

<data:DataGrid.Columns>    <data:DataGridTemplateColumn Header="Broker">        <data:DataGridTemplateColumn.CellTemplate>            <DataTemplate>                <TextBlock Text="{Binding Moniker.Abbreviation}"                           ToolTipService.ToolTip="{Binding Moniker.Name}" />            </DataTemplate>        </data:DataGridTemplateColumn.CellTemplate>    </data:DataGridTemplateColumn></data:DataGrid.Columns>

In this example Moniker.Abbreviation is displayed in the column. When the user hovers over a cell, the full broker name (Moniker.Name) is displayed in the tooltip.

Note: This example was taken from a Silverlight 3.0 application.