If DataItem implements IHasAttributes, this gets the Attribute value for the dataitem using DataField as the Attribute.Key. Otherwise, it will look in the grid.ObjectList[key] using the DataField as the lookup key. Example: If using a Person Grid, the value of the Attribute "FavoriteColor" would be shown in the grid by specifying this grid column <Rock:AttributeField DataField="FavoriteColor" HeaderText="Person's Favorite Color" />