Since most journeys by train from the UK go via Paris, we've penned a quick guide to changing trains in Paris. These are the most common interchanges, i.e from Gare du Nord, but if you want advice on another route just ask.

Useful links:

Paris Metro Map

Metro route planner

Loco2 Cycle Scheme post

From Gare du Nord to...

Gare de l'Est It's an easy-peasy ten minute walk. Here's a map for you

Gare de Lyon At the end of the Eurostar platform look for signs to the RER line D. Once you've bought your ticket follow the signs to 'RER D direction Melun / Malesherbes'. So long as you're heading the right direction, all the trains on this line stop at Gare de Lyon. The trip takes around 7 minutes, and there's just one stop on the way - Chatelet-les-Halles. The whole journey between stations should take no longer than 25 minutes.

Gare d'Austerlitz
As you approach the end of the Eurostar look for signs to the Metro Line 5, direction Place d'Italie. It's direct line and should take you around 20 minutes.There are 9 stops between you and Gare d'Austerlitz. The exit from the Metro is opposite the main entrance to the station.

Gare de Bercy At the end of the Eurostar platform, bear left and look for RER line D. Follow the signs for 'RER D direction Melun / Malesherbes' and stay on the train for the short ride to Gare du Lyon (as above). Once there you can opt to complete the last 1km on street level on foot or by taxi, or board the Metro line 14, direction Olympiades and go one stop to Bercy.

Gare Montparnasse Follow signs from the Eurostar to the Metro, looking out for signs to Metro line 4 direction Porte d'Orleans. This is a direct line which will take you to Montparnasse Bienvenue in a little less than 25 minutes. You should note though, that compare to the other routes, there's a bit of a walk and stairs between the Metro at Montparnasse and the mainline station. If you've got a lot of luggage (or children!) you might want to consider getting a taxi the last 700 metres.

One word of warning for the Gare de Lyon - Gare du Nord RER connection: the service is not so regular (every 10-15 minutes or so) during the evening. It's sometimes worth getting to Chatelet and changing there if you're on your way to catch a late Eurostar home to London.

There is of course the option of changing in Lille rather than Paris, although the Lille - South of France TGVs tend to stop all over the place, so a change in Paris tends to end up being quicker.

I learnt something useful last week. On our way to Chamonix last week I discovered that you can buy a carnet of Metro tickets from the restaurant car on the Eurostar. It costs around €15, which is a slight mark-up on the usual €12.50 but definitely worth it if you're in a rush to catch you next train.

A carnet is a book of ten one-way Metro tickets, called 't' tickets, which are valid for a single trip between any two Paris Metro stops, and the RER. They are usually €1.70 each so it's a good saving if you're travelling in a group, and you can save some for the return trip too.

Ah, I wasn't aware of the markup on the Carnet. Crafty!

In my experience if you use a ticket machine at the RER station in Gare du Nord the queues are small, while the queues can be huge at the Metro station. Tickets bought at one work at the other.

The only question about carnets though: how long are the tickets valid? Do they expire?

Carnet tickets for the Metro/RER in Paris do not expire. It can happen that they do not work if you have kept them for a long time (they are magnetic) but, if this happens, you can go to the ticket selling counter or the information counter of any metro stop in Paris and ask them to replace them (this replacement is free).

Elio, a warm welcome to the forums. Nice to have you on board, if you'll excuse the train pun :) Thanks so much for the tip. I just learned something (and actually I have a ticket from my last Paris trip that I haven't used) so it's good to know!