Charles de Gaulle to Rouen

There's no direct train service between CDG and Rouen, you have to go into Paris and get a train at Gare St-Lazare. These trains leave frequently and you won't need an advance reservation. This website shows train times. "Paris St-Lazare" is the start and "Rouen Rive Droite" is your likeliest end point.

The easiest way to get from CDG to Gare St-Lazare is by taxi, which will cost 50 euros for up to four people. A cheaper way is the RER "B" line to Chatelet, a walk underground to Metro line 14, and the Metro to Gare St-Lazare. The RER-Metro route will cost less but requires more baggage handling in stations. Which route is faster depends partly on time of day (congested highways at rush hours) and partly on how fast you can transfer with bags on and off the trains.

Hi Karen -- I will adapt most of my answer from another recent thread on the same subject (though in that case the OP was considering a private driver):

There are no good routes from CDG airport to Rouen that bypass Paris, so you will have to go into Paris to make this rail connection. (If you search for direct CDG-Rouen tickets, you get routings via places like Lille, which is an incredible detour out of your way.)

The train to Rouen leaves from Gare St-Lazare in Paris. To get from CDG to Gare St-Lazare, you can:

• Take the RER (regional express rail): you would take the RER B from CDG to Gare du Nord, then switch to the RER E and take it one stop from Magenta to Haussmann–St-Lazare, and then walk up to the Gare St-Lazare mainline railway station. This will run you €10.30 per person.
• Take a cab from CDG to Gare St-Lazare. There is a flat fee of €50 from the airport to the Right Bank of Paris, which is where Gare St-Lazare is located. Make sure to take a legal, legitimate taxi from the taxi queue (strictly ignore any touts or anyone waving signs or shouting at you at the airport).

Paris to Rouen trains start at €10 per person for advance-purchase, inflexible tickets (i.e. if you miss the train that you bought a ticket for, your ticket is worthless). If you're hesitant to commit to a particular train or are worried about making a same-day air-rail connection via Paris, you can opt to walk up and buy tickets once you arrive at Gare St-Lazare, but be aware that the last-minute price for those can be up to €27 per person.

I have departed from Gare-Saint-Lazare many times after landing at CDG. As a solo traveler, I find the easiest way is to take the RoissyBus. It leaves right outside of arrivals at CDG, and drops you off next to the Opera Garnier (7-minute walk to the train). 12€ per person, no stairs, no changes, etc. I've never taken a taxi, but if you had 3–4 people, I would think that would be fine as it is a flat rate of 50€ for up to four people, and it is door-to-door. Both are more direct, and less of a hassle than the RER/Metro hassle.

Thank you very much for your replies. Since there is just myself and my husband the 50 Euros is a little steep. We will get there the other way suggested.