http://msdn.microsoft.com/en-us/library/bb397895.aspx msdn.microsoft.com/en-us/library/bb397895.aspx http://msdn.microsoft.com/en-us/library/bb397895.aspx left outer join How to: Perform Left Outer Joins (C# Programming Guide) Left Outer Join DefaultIfEmpty() LOJ perform an outer join with LINQ Left Outer Join msdn.microsoft.com/en-us/library/bb397895.aspx