Charles de Gaulle is 26 km north-east of central Paris, and after a long flight the last thing you want is to figure out transport with suitcases in hand. Here is every option, honestly compared.
RER B train — cheapest, not easiest
The RER B suburban train runs from Terminals 2 and 3 to Gare du Nord, Châtelet and Saint-Michel in about 35 minutes, for roughly €12 per person. It's the budget choice, but be realistic: stairs and crowded carriages with large luggage, frequent weekend engineering works, and you'll still need a metro connection or a walk to reach your hotel. Late at night the service stops, and early flights before 5 am can't use it at all.
Official taxi — the airport queue
Paris taxis charge a regulated flat fare from CDG — around €56 to the Right Bank and €65 to the Left Bank. The catch is the queue: at peak arrival times it can take 30–45 minutes to reach the front, and no, the driver was not expecting you.
Bus — cheap but slow
The Roissybus runs to Opéra for about €17 and takes 60–75 minutes depending on traffic. Fine for a solo traveller with one bag and no schedule; painful for a family after a red-eye.
Private transfer — door to door, price known in advance
A pre-booked private transfer costs €79 for up to 3 passengers or €115 for up to 7 — per vehicle, not per person. Your driver tracks your flight, waits in the arrivals hall with your name, and drives you directly to your hotel door. For two or more people the price difference with a taxi almost disappears, and the queue, the connections and the uncertainty do disappear.
Which should you choose?
Travelling alone, light, mid-day, on a budget: take the RER B. Two or more people, luggage, children, a night arrival or an early departure: a private CDG transfer is the option travellers regret not booking. Fixed price, confirmed in advance, and the driver adapts to your real landing time for free.