From Roissy Charles de Gaulle Airport :
Bus Air France : The line 4 of the Air France Bus connects the airport of Roissy Charles de Gaulle and Gare de Lyon. Buses circulate every 30 minutes, 7 days 7, from 06:00 to 22:00.
RER B : down at Châtelet-Les Halles station, and RER A down at Gare de Lyon station.
From Orly Airport :
Metro Orlyval: down at Antony station, then RER B down at Châtelet-Les-Halles station, then RER A down at Gare de Lyon station.