How do I transfer between train stations in Paris? (Gare du Nord, Gare de Lyon, Gare Montparnasse, etc.)

Paris has several main train stations, all serving national and international trains to different parts of the country. When travelling through Paris by train it is almost always necessary to change from one station to aother.

Gare du Nord: Eurostar high-speed trains to London, Brussels, Amsterdam and Germany. Ouigo-trains to Brussels, high-speed TGV trains to Lille and other cities in the north of France. Regional trains.
Gare de l'Est: TGV high-speed trains trains eastward to Nantes, Strasbourg. International TGV and ICE high-speed trains to Luxemburg and Germany. Nightjet sleeper trains to Vienna and Berlin.
Gare de Lyon: TGV high-speed services to the South and Southeast, including Lyon, Annecy, Marseille, Nice, Monaco, Toulon, Perpignan. International high-speed TGV trains to Spain and Switzerland.
Gare de Montparnasse: All TGV and other trains to Western France (Nantes, Rennes, Brest), Southwest (Bordeaux, Toulouse, Hendaye, Pau).
Gare d'Austerlitz: All Intercités de Nuit French sleeper trains. Daytime intercity trains to Clermont-Ferrand. Regional trains.

How to transfer between stations & how to buy tickets

Frequent metro, RER (express metro) and/or bus lines connect all stations with each other. Connections are available 24/7 and often run every few minutes. No need to pay for an expensive taxi!
It is easy to simply use your smartphone's Google Maps or Apple Maps function, which both generally have up-to-date information on transport options in Paris. Simply navigate to the station you need to go to.
Parisian public transport is run by RATP. For tickets simply download the RATP and SNCF apps to buy tickets on your phone with your credit card. Use your phone's NFC function to use the tickets at metro stations or in busses.
If you don't have a smartphone with NFC, a paper NAVIGO pass can be bought from ticket machines at every train station or metro stop, which can be topped up with money as you travel.
A single ticket between any two train stations as described above usually costs €2.50.
Although the metro or bus journeys between any two train stations takes no longer than 20 or 25 minutes, add an extra 20 minutes or so for walking from the metro stations to the platform of your train.
We generally recommend planning at least 75-90 minutes to transfer in Paris, to allow time for delays, finding the right metro line and platforn, and for buying tickets if necessary.

Single use metro tickets are being phased out, with the top-up Navigo pass being the best alternative if you have no phone with internet and NFC functions. It used to be possible to buy single tickets on board of TGV and Eurostar trains, but this is slowly being phased out.

Which lines to take

It is easiest to simply use your smartphone's Google Maps or Apple Maps function, which both generally have up-to-date information on transport options in Paris. Simply navigate to the station you need to go to.

From Gare du Nord / Gare de l'Est: These stations are a 10-minute walk from each other.

To Gare de Lyon: RER line D from Gare du Nord, total travel time around 20 minutes. From Gare de l'Est first walk to Gare du Nord (10 minutes).
To Gare d'Austerlitz: Metro line 5 (direction Place d'Italie), total travel time 25 minutes.
To Gare Montparnasse: Metro line 4 (Direction Bagneux), total travel time 35 minutes.

From Gare de Lyon:

To Gare du Nord / Gare de l'Est: RER line D to Gare du Nord, total travel time 20 minutes. For Gare de l'Est walk another 10 minutes.
To Gare d'Austerlitz: 8-minute walk.
To Gare Montparnasse: walk to metro stop Bercy, from there take Metro line 6 (direction: Charles de Gaulle), total travel time 35 minutes.
- Alternatively, less walking: bus line 91, total travel time around 45-50 minutes.

From Gare d'Austerlitz

To Gare du Nord / Gare de l'Est: Metro line 5 (direction: Bobigny), total travel time 25 minutes.
To Gare de Lyon: 8-minute walk.
To Gare Montparnasse: Bus line 91, total travel time around 40 minutes.
- Alternatively take metro 5 to Place d'Italie, change for Metro 6 (direction: Charles de Gaulle) to Gare Montparnasse, total travel time 30 minutes.

From Gare Montparnasse

To Gare du Nord / Gare de l'Est: metro line 4 (direction: Porte de Clignancourt), total travel time 35 minutes.
To Gare de Lyon: Bus line 91, travel time around 40 minutes.
- Alternatively: metro line 6 to Bercy, walk 10 minutes to Gare de Lyon. Total travel time 40 minutes.
To Gare d'Austerlitz: bus line 91, total travel time 35 minutes.
- Alternatvely: metro line 6 to Place d'Italie, change for metro line 5 (direction: Bobigny) to Gare d'Austerlitz. Total travel time 35 minutes.