London Overground ( LO ) is a commuter rail service in London , UK . The London Overground name is the brand , which is used by the Transport for London ( TfL ) for train services on four railway lines in the London area : the Euston-Watford DC Line , the North London Line , the West London Line and the Gospel Oak to Barking Line . A peculiarity of this part of the network is that at the London Overground line runs below the London Underground line .