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A one way ticket on the metro now costs €1.50, allowing for one journey to any point on the network (and including any necessary connections). A better option is to buy in bulk - ask for a carnet (pronounced ‘car-nay’) and you’ll receive ten tickets at a discounted rate of €11.10. The tickets don’t become active until stamped at the turnstile on your way to the platforms - so it’s perfectly sensible to carry a few spare with you as you hop around the city.

You can also use the ticket on Paris’ buses, provided you remember to validate it in the stamping machine on board - your ticket is now valid for an hour and a half after you first get on, allowing you to hop between buses as required to reach your destination, though you can’t connect between metro and bus on the same ticket.

Single tickets and carnets are sufficient for most visitors to the city - but if you really intend to use the metro heavily during your visit the Paris transport authority (the RATP) also offers a range of travel cards. The Paris Visite card is aimed at tourists, and will allow unlimited travel on the metro and bus system for 1-5 days, depending on the length of ticket you buy. It’s fairly pricey, and you’d need to use the system an awful lot to get full value from the price, but you might consider it worthwhile for the freedom to move around the city as and when you please.

If you’re on the tightest budgets, there are cheaper options than the Paris Visite tickets - the mobilis ticket, in particular, offers a whole day’s transport for a few euros less than the equivalent Paris Visite. The only significant difference is that it’s marketed at Parisians, not foreign tourists, and indeed you wont find any mention of it on the English-language pages of the Metro website.

If you’re staying longer than a week (or moving to Paris long term) you’d be wise to get a Carte Orange - which offer unlimited travel on a weekly or monthly basis, and which start at €15 for a week’s travel within the central zones. Carte Orange fares operate over a calendar month, or indeed on a monday to sunday basis - if you buy it on a thursday, then, it will still expire late on Sunday night. You’ll need to hand over a passport photo for the travel card. You can get all the details on the RATP website.