This may be a boring post for most of you but having been in France for six months now I think I've just about managed to suss out the mysteries behind the Parisian train tickets. With Paris being such a popular destination I thought it may come in handy for some of you!
So, a quick overview: there are a variety of train types but the two you will use in Paris are the RER and Métro; Paris has different zones (similar to the London underground) central Paris being in zones 1-2 and the outskirts 3-5. These are your options:
The best ticket I've found by far is the billet jeune this one is for young persons under the age of 26 which gives you unlimited travel between the zones of your choice, starting at 3,60€ for zones 1-2. See all pricing here. The downfall? It's only available on weekends and French bank holidays.
Next, comes the Mobilis. This one is a little more expensive but is valid on weekdays as well as weekends and again, entitles you to unlimited travel between the zones of your choice starting at 7,70€ for zones 1-2. This ticket can be used by adults and there is also a demi-tarif (discounted rate) for children under 10. See all pricing here.
The most widely advertised is the Paris Visite which is aimed at tourists, although I must admit I personally don't think it's amazing value for money. Prices start at 11,15€ for unlimited travel within zones 1-3 and a discounted rate is available for children. An advantage of the Paris Visite is that you can buy tickets that last up to 5 days at a discounted rate. See all prices here.
Very similar to Mobilis but more expensive (a Mobilis ticket between zones 1-3 is 9,30€) and the only reason I've found for that is that Paris Visite comes with a little booklet of discounts which you can use at some of the main tourist attractions in Paris including museums and the Arc de Triomph, however, for European citizens under the age of 26 the vast majority of museums and attractions such as the Arc de Triomph are actually free if you have a European ID and you're also likely to find good discounts online especially for the Bateaux Parisiens. If anything, I would do a little bit of research on which sites are free for EU citizens and decide from there whether or not the extra euros for this ticket are worth it.
Finally, for travel on the Paris metro there is the t+ which are tickets for use on the métro, you can buy 1 ticket at 1,80€ or a carnet (book of 10) for a discounted rate. These are good if you only need to use the métro once, and I believe they're valid for up to 1hr30 after the first use so you could squeeze in a return journey in one ticket if you're quick enough! See prices here.
There is also the origine-destination ticket, you'll probably be least likely to use this but it's worth mentioning too. This is if you are travelling outside the city of Paris but still staying in the Parisian zones (for example, from zone 1 to 5 or zone 4 to 5) you basically use this if you can't use the métro and don't have any of the tickets mentioned above valid outside métro zones. The pricing varies entirely on the journey but you can calculate the price here.
I hope this comes in handy for any of you visiting Paris, I found myself endlessly searching for the best value tickets and the difference between them so I thought it would be useful to have this post up in English (as most of the ticket info, other than for the Paris Visite ticket, is in French so some of you may not have come across it before). Really hope this has helped!
Prices stated are correct as of 2015 - check the pricing links for any changes.