Taking your bike on a train in France

French Railway services are divided into two groups: Grandes Lignes (main line) and TER (regional services). The two services work together and in practice there is no difference between the two groups. If you only wish to travel a short distance you can click on a link on the SNCF home page (www.voyages-sncf.com) that leads to a map of France to allow you select your region of interest. Not all but some of the main line services will take bicycles, including some of the high speed TGVs, whereas about 95% of all regional trains do. You can find out which mainline trains take bikes by clicking on conditions of service (in French) or check the SNCF bike site as well (in French). The English language conditions of service do not mention this. Probably no Frenchman expects les Rostbifs to know anything about cycling. If there is room in your train of choice you can pop your bike on the train and away you go. You can also reserve bike places on long distance trains beforehand. The local TER trains do not accept any form of reservation, but bicycle transport is free. One word of warning though, mainline trains do not take tandems. However we would recommend that when travelling on the TGVs that you reserve bike places. Not only are there but few, but also bikes block 4 additional seats that can be used by travellers without reserved tickets, of whom there can be quite a few. They are not likely to give up their seats unless you can wave your reservations under their nose.
It is suggested in various websites and downloads that one should use the German Railway website www.bahn.co.uk to find trains in France that offer places for bikes. The German Railways website offers a button “Transport of bicycle required” so you can filter out all the trains that do not transport bikes beforehand . However any database is only as good as the data put in it. Unfortunately www.bahn.co.uk only recognises that the TGVs running between Paris, Strasbourg and Munich can carry bikes. All the other TGVs are assumed not to carry bikes. In addition there is no mention at the time of writing that at least one extremely useful sleeping car train from Paris to Toulouse takes bicycles. We would suggest you use www.voyages-sncf.com for your preparations. Obviously this situation could change in future.
If these thoughts are not enough click on http://www.crazyguyonabike.com/doc/CyclingInFrance to find Leo Woodland's guide to cycling in France with a good description of the perils and pleasures of taking le train with your velo.