Fuhget aboutit, it's only a euro. Do it the easy way.

It's 1.25€ per person each way. For me, that's 12.50€ - easily worth the two minute investment in time.

Robespierre, if you are able to reach one of the Issy's RER stations from one of Issy's metro stations by foot in 2 minutes or less, don't forget to apply for the next olympic games ! ;-)

Who's talking about Métro stations? (Besides you?)

As I said above:
Ride the RER to Issy
Get off
Buy an RER ticket to Versailles
Get on the next RER train

...see? No mention of Métro.

norween - I don't want to beat a dead horse and I especially do not want to argue to argue with someone who lives in Issy and who knows firsthand that you need a zone 3 ticket. But the map at ratp.fr shows both Issy RER stations as being in zone 2. Why is that?

I haven't read all the replies, especially those at the end relating to Versailles.

However, we were just in Paris last month. We purchased the Carte Orange at the Ecole Militaire station (we brought along our photos instead of trying to find a photo booth).

Going to Versailles, I have done it two ways. I either purchase the RER tickets at the Ecole Militaire station (if there's no line) and transfer at Invalides or I go directly to Invalides and use the machine at the RER entrance to purchase the tickets.

The only rudeness we encountered during our month in Paris was when we took our existing Carte Orange to the woman at the Ecole Militaire Metro and asked for tickets for the following week. She refused to sell to us, and had done so to the American couple in front of us. Then, fortunately, we saw the machine which dispensed the tickets. But if you are buying your initial Carte Orange, go to the Bir-Hakim metro, where they do a lot of business, and we were treated very well indeed.