Tickets can be bought in carnets of ten from any station or tabac showing a green métro ticket sign; the cost is ?8.38, as opposed to ?1.23 for a single ticket. Only one ?1.23 billet is ever needed per journey on the métro system. It's also valid for any journey within zones 1 and 2 on the RER or by bus, but you cannot switch between buses or between bus and métro/RER on the same ticket. Night buses require separate tickets costing ?2.29 each, unless you have a weekly or monthly travel pass. For RER journeys beyond zones 1 and 2, you must buy an RER ticket; visitors often get caught out, for instance, when they take the RER instead of the métro to La Défense. Children under four travel free and from four to ten at half price. 


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Be sure to keep your ticket until the end of your journey: you'll be charged a stiff fine on the spot if you can't produce one. 
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If you've arrived early in the week and are staying three days or more, it may be more economical to obtain a photocard, the Carte Orange (you'll need a passport photo - available from the booths in the main stations), with a weekly travelcard, known as a coupon hebdomadaire ; you'll probably want one for zones 1 and 2 to cover the city and inner suburbs. Costing ?12.50, the zone 1 and 2 version is valid for an unlimited number of journeys from Monday morning to Sunday evening, and is on sale at all métro stations and tabacs. You can only buy a travelcard for the current week until Wednesday; from Thursday you buy a coupon to begin the following Monday. You need to write your Carte Orange number on the travelcard. There's also a monthly pass ( mensuel ), costing ?42.53, for zones 1 and 2. A word of warning: the Carte Orange is technically for Île de France residents only, though most clerks will sell you one as a visitor. 

Other options include the Paris Visites , 1-, 2-, 3- and 5-day visitors' passes at ?7.62, ?12.20, ?18.29 and ?25.91 for Paris and inner suburbs, or ?15.24, ?26.68, ?37.34 and ?45.73 to include the airports, Versailles and Disneyland Paris (make sure you buy this one when you arrive at Roissy Charles de Gaulle or Orly to get maximum value). A children's version is available at half price for 1, 2 or 3 days. The main advantage of Paris Visites passes is that, unlike the coupon hebdomadaire , whose validity runs unalterably from Monday to Sunday, they can begin on any day. They also allow you discounts at certain monuments, museums, shops and restaurants. 

Both the Carte Orange and the Paris Visites entitle you to unlimited travel (in the zones you have chosen) on bus, métro, RER, SNCF and the Montmartre funicular. On the métro you put the coupon through the turnstile slot, but make sure you return it to its plastic folder. On the bus you show the whole carte to the driver as you board - you don't put it into the punching machine. 

A mobilis day pass is also available, taking in all forms of RATP transport (from ?4.57 for the city, ?10.67 to include the outer suburbs and airports).