At the airport, follow the Baggage-Exit signage then indications for Trains RER B.
Take the RER Line B to Saint Michel–Notre Dame (all trains call at Saint Michel–Notre Dame).
At Saint Michel–Notre Dame, change for the RER line C to Gare d’Austerlitz (one stop).
At Gare d’Austerlitz, take the RER line C to Saint Michel–Notre Dame (one stop).
At Saint Michel–Notre Dame, change for the RER Line B (Direction Aéroport Charles de Gaulle).
Depending on your terminal, get off at station Aéroport Ch. de Gaulle 1 or Aéroport Ch. de Gaulle 2.
At the airport, proceed to your departure terminal.