The RER (ɛʁ.ə.ɛʁ; Réseau Express Régional, `Regional Express Network`) is a regional rapid transit system in France serving Paris and its suburbs. The RER is an integration of a modern city-centre underground rail and a pre-existing set of commuter rail lines. It has several connections with the Paris Métro within the city of Paris. With..... Found on http://en.wikipedia.org/wiki/RER