Difference between two lists

Question

I Have two generic list filled with CustomsObjects.

I need to retrieve the difference between those two lists(Items who are in the first without the items in the sec

Answer 1

List _list_DF_BW_ANB = new List();    
List _listA = new List();
List _listB = new List();

foreach (var itemB in _listB )
{     
    var flat = 0;
    foreach(var itemA in _listA )
    {
        if(itemA.ProductId==itemB.ProductId)
        {
            flat = 1;
            break;
        }
    }
    if (flat == 0)
    {
        _list_DF_BW_ANB.Add(itemB);
    }
}