Getting to CDG airport from Gare de Nord in Paris

It's the RER "B3," make sure it says CDG airport on the front. There's another "B" that doesn't go to the airport.

The Paris by Train website has all the info you'll need about tickets and schedules. It's a very easy trip, but keep an eye out for pickpockets especially at the station.

Thanks Dick I appreciate your help Stew

I recently made the trip. Signage is good so it is an easy trip to make.

Make sure you know which of the two stops is most convenient to your airline. There are two stops at the CDG airport. RER stop #1 is for CDG terminal 3. RER stop #2 is for CDG terminal 2. This page lists the terminal each airline operates from.
http://easycdg.com/airport-guide/which-terminal-paris-cdg-airport-charlesdegaulle/

Trains run every 6 to 15 minutes. It takes 35 minutes and tickets are 10 euros and they can be bought from the machine with coins or credit card.
http://easycdg.com/transport/charles-de-gaulle-airport-cdg-to-paris-by-rer-train/

Here is a map of the RER line from Paris to CDG
http://www.about-paris.com/rer-b-paris-to-cdg-plan.htm

This map shows the stops and provides a little more terminal information
http://www.experienceloire.com/cdg-plan.htm

Thanks Greg that helps a lot. Just about ready to leave for Europe this morning. It has been awhile

The RER trains use the right side of Gare du Nord, as you face the station. There are two escalators down to the tracks in that section; use the left-hand one to get to the correct platform. The signs are not very clear. Paris by Train is always helpful because the photos help with orientation. Keep your ticket to go through the exit gate at CdG. (PS: Hello from Windsor.)