Paris is a very safe city, though you might come back from a metro ride and realize that your wallet was stolen :-(

No violence, but it is very unpleasant!!!

It happened to me, to people I work with, and to my guests...

You can learn more on this page

Often pick-pockets are young, like thirteen years old, and not French...

So, pls, hide your wallet properly, do NOT use an iphone or anything similar in the metro.

Some general pieces of advice:

1.  Passport Photos:  Bring an extra set of passport photos on your trip.  It is difficult to find a place to have photos for US passports in Paris and is costly.
2.  Money:  Don't carry a lot of cash.  Use the ATMs and your credit cards.
3.  Passports:  Leave your passport in the apartment.
4.  Copies of Important Documents:  Bring copies of important documents, your credit cards, etc on your trip and leave another copy with friends at home.

In any case, you can have your passport replaced at the US embassy, which is located right off the metro stop Concorde,
2 Avenue Gabriel
75008 Paris, France
01 43 12 22 22
http://france.usembassy.gov/passports.html