Paris: one-month all-purpose transit pass?

The problem with Paris is that to dissuade tourists from using term passes the dates are very inflexible. A one-month pass is only available starting on the 1st of a calendar month, and a one-week pass only for a calendar week Mon-Sun. You might want to plan to arrive early in the month to take full advantage of a pass. Passes cover bus, tram, metro and RER. A standard central zone pass will cover all of arrondisements 1-20.

The only monthly pass is the Navigo Decouverte. You can read on all tickets and passes on this site: http://www.vianavigo.com/en/tickets-and-fares/
the Navigo 'mois' is the monthly version...

Yes, the Navigo Decouverte is the way to go. Bring a 25 mm by 30 mm passport type photo of your self when you buy to save time. You can get at the CDG RER train station when you arrive in Paris. Goes by calender month for the "mois" pass or Monday morn to Sunday night for the "semaine" weekly, so it is advantageous to arrive early in the month. If you arrive mid month, just get the weekly option and reload every week for not much more. Zones 1-2 and buy airport or Versailles tickets separately unless you plan on a lot of trips to the 'burbs as the all-zone pass is 75% more than the 1-2 zone which covers all of Paris proper.

Thank you, everyone! All of you information is very much appreciated. We're staying for an entire calendar month, so it sounds like that was a fortunate choice we made.

For the photo you can just make a color copy of your passport picture, and reduce it to the approximate size.

Thanks, Karen. I was going to get passport photos taken, so you've just saved me about $20!