Just want to chime in to say that using a broker to buy index funds should be possible in France as well. I'm in The Netherlands and use DeGiro[1] which is available in France as well, so that might be an option. My investment portfolio basically consists of a few index funds, all can be bought once per month with this broker without a brokerage fee.

As for tax-efficient ways, my french isn't that good so I don't know the details but if I understand this topic [2] correctly you should have some options like PEA, PERCO/PERP, and/or PEE/PEI/PEG

N.B.: There will always be some discussion around this specific broker because their 'default account' contains a clause where this broker is allowed to temporarily loan your assets to other customers. Don't do this. You can get a so-called 'custody account' (which is basically a regular brokerage account) that's only marginally more expensive.

[1]: https://www.degiro.fr [2]: http://redd.it/3oht1m/

Open an investment account in the USA - it's fairly straightforward. I don't know your tax system in france, but you can invest in the US as an individual or an entity, probably worth talking w/ a tax attorney about how to do it - it's certainly done by others.

France doesn't have an ISA/Roth IRA/TFSA equivalent? Google tells me - PEA (Plan d'Epargne en Actions) - but this info was from 2006.

Invest in a cheap French or Eurozone total market index fund. It only makes sense to invest in a fund that matches your local currency.