How do I Aggregate multiple IEnumerables of T

Given.... ``` Public MasterList as IEnumerable(Of MasterItem) Public Class MasterItem(Of T) Public SubItems as IEnumerable(Of T) End Class ``` I would like a single IEnumerable(Of T) which will iterate through all SubItems of all MasterItems in MasterList I would like to think that there is a Linq facility to do this, or an extension method I am overlooking. I need a mechanism that works in VB9 (2008) and hence does not use Yield.