If you’re planning on visiting more than one museum in a few days you might want to get the Museum Pass (Carte Musée et Monuments), which not only offers a discount, but let’s you avoid the invariably long queues outside the major museums. It’s good at 70 different museums and monuments.

The cost depends upon how many days you need.
1 day = €13
3 day = €25.20
5 day = €39

The pass doesn’t include special exhibitions, which have an extra charge.

Tickets can be purchased at:
participating museums and monuments
major metro stations
Paris Tourist Bureau
FNAC tickets counters
Or when you buy a railpass in your home country

More info at: https://www.intermusees.com/