Battles amongst American visitors to Paris have broken out over this question. After all, in the U.S., it’s customary to leave a 15 to 20% tip for your waiter or waitress after eating at a restaurant. That’s because these hard-working folks earn their living from their tips, since their salaries fall below the minimum wage (and mostly go to cover taxes). In Paris (as in most of Europe), waiters and waitress earn a fare wage. And a service charge is typically (and legally) added to your bill at restaurants, bars, cafés, etc. That said, it’s good manners to leave an additional 2 or 3% for your server, to show your appreciation.
What about taxis, you ask? You can tip up to 15% extra for them, but it’s not expected. And at the hotel, you should leave the housekeeping staff a Euro or two for each day of your stay.